Was it reckless to allow Wormtongue to go free?

Question

When Grima Wormtongue is evicted from Theoden's court in The Two Towers he is given free leave to go wherever he wants. Gandalf, Theoden and the whole company are in no doubt that he is a plant of Saruman's who, once exposed, will presumably be quite keen to return to his true master's side (as indeed he does).

In the movie Theoden goes to strike Wormtongue down only to have his hand stayed by Aragorn, who says, "No, my lord. Let him go. Enough blood has been spilt on his account." Wormtongue then goes back to Saruman and tells him about the hidden weakness in Helm's Deep, which in turn leads to half the wall being blown up. Countless men and elves die and Isengard gets to within a whisker of victory.

Great decision, Aragorn.

This seems like a glaring plot hole in the film. But it is hardly less so in the books. True, the weakness in the wall may have been found without Wormtongue anyway. The explosion in the books is attributed by Aragorn only to "devilry of Saruman" and isn't tied to Wormtongue himself. Yet, even when you put Helm's Deep to one side, Wormtongue was a known rogue agent. Surely he was capable of causing greater harm to Rohan - and of being a greater aid to Saruman - when let loose? Indeed, he went on to cause a great deal of mischief in the Shire, proving himself to be a dangerous and slippery individual.

In the books they discuss a number of different options for Wormtongue. He asks that he be left in charge of Edoras. Understandably, that request is rejected out of hand. Theoden suggests sending him into battle:

"You have my pity," said Theoden. "And I do not send you from my side. I go myself to war with my men. I bid you come with me and prove your faith."
_{(The Two Towers, Chapter VI, The King of the Golden Hall).}

I can't understand the rationale for this suggestion. Surely Wormtongue already 'proved his faith' (or lack of it) when he tricked and enslaved Theoden's mind for Saruman. They already know he's untrustworthy. If they send him to war, that he would betray them seems inevitable. Gandalf seems to recognise this.

"See, Theoden, here is a snake! With safety you cannot take it with you, nor can you leave it behind. To slay it would be just. But it was not always as it now is. Once it was a man, and did you service in its fashion. Give him a horse and let him go at once, wherever he chooses. By his choice you shall judge him."
"Do you hear this, Wormtongue?" said Theoden. "This is your choice: to ride with me to war, and let us see in battle whether you are true; or to go now, whither you will. But then, if ever we meet again, I shall not be merciful."
_{(The Two Towers, Chapter VI, The King of the Golden Hall).}

So the danger of leaving him behind or sending him to war is obvious. Again, there's surely no need to see whether he is "true" or not since he's already been revealed as a traitor. Why didn't they consider the obvious course - taking him to Helm's Deep with them as a prisoner and keeping him locked away in some dark corner until the battle was over?

Why let him go free where he could cause further damage?

Ideally, I'd like an answer that references both the book and the film.

Answer 1

There is always some risk in being merciful

The question quotes the discussion between Théoden and the others about what to do with Wormtongue. It is clear from that discussion that they are aware that Wormtongue may cause problems if he is allowed to go free. Théoden lets him go as an act of mercy in recognition of his earlier service, giving him one last chance to reform.

Imprisoning Wormtongue

The last part of the question asks why Wormtongue wasn't simply taken to Helm's Deep as a prisoner. This does at least seem a logical choice, and is not really addressed in the discussion. I suspect that Gandalf would point to the power of Wormtongue's tongue (he may have learned a little from Saruman). We know that his words were enough to poison Théoden's mind so that he was enfeebled. In The Houses of Healing, Gandalf tells Éomer that Wormtongue was able to infect Éowen (so that she was ready to throw away her life).

‘Think you that Wormtongue had poison only for Théoden’s ears? Dotard! What is the house of Eorl but a thatched barn where brigands drink in the reek, and their brats roll on the floor among their dogs? Have you not heard those words before? Saruman spoke them, the teacher of Wormtongue. Though I do not doubt that Wormtongue at home wrapped their meaning in terms more cunning. My lord, if your sister’s love for you, and her will still bent to her duty, had not restrained her lips, you might have heard even such things as these escape them. But who knows what she spoke to the darkness, alone, in the bitter watches of the night, when all her life seemed shrinking, and the walls of her bower closing in about her, a hutch to trammel some wild thing in?’

_{The Lord of the Rings Book Five, Chapter 8: The Houses of Healing
Page 867 (Houghton Mifflin Harcourt; Single Volume 50th Anniversary Edition)}

This would be part of what Gandalf has in mind when he says of Wormtongue "With safety you cannot take it with you, nor can you leave it behind." So imprisoning Wormtongue would also be dangerous.

Let's look at the consequences of the decision to free him:

The culvert at Helm's Deep

Wormtongue's role in blowing up the culvert in the movie is just an unnecessary detail made up by Jackson (it isn't mentioned in the books). Even if this information came from Wormtongue, there is no reason to assume he told Saruman about it after being released (as mentioned in Edlothiad's answer). I don't consider this a consequence of the decision to free Wormtongue

The Palantír

During the parley at Orthanc, it is Wormtongue who throws the Palantír at Saruman or Gandalf.

At that moment a heavy shining thing came hurtling down from above. It glanced off the iron rail, even as Saruman left it, and passing close to Gandalf’s head, it smote the stair on which he stood. The rail rang and snapped. The stair cracked and splintered in glittering sparks. But the ball was unharmed: it rolled on down the steps, a globe of crystal, dark, but glowing with a heart of fire. As it bounded away towards a pool Pippin ran after it and picked it up.

‘The murderous rogue!’ cried Éomer. But Gandalf was unmoved. ‘No, that was not thrown by Saruman,’ he said; ‘nor even at his bidding, I think. It came from a window far above. A parting shot from Master Wormtongue, I fancy, but ill aimed.’

‘The aim was poor, maybe, because he could not make up his mind which he hated more, you or Saruman,’ said Aragorn.

_{The Lord of the Rings Book Three, Chapter 10: The Voice of Saruman
Page 583-4 (Houghton Mifflin Harcourt; Single Volume 50th Anniversary Edition)}

Using the Palantír, Aragorn is able to learn the state of Sauron's preparation for war and to distract Sauron. This leads him to try the desperate journey through the Paths of the Dead. When he tells Gimli and Legolas about revealing himself to Sauron, we read:

‘The hasty stroke goes oft astray,’ said Aragorn. ‘We must press our Enemy, and no longer wait upon him for the move. See my friends, when I had mastered the Stone, I learned many things. A grave peril I saw coming unlooked-for upon Gondor from the South that will draw off great strength from the defence of Minas Tirith. If it is not countered swiftly, I deem that the City will be lost ere ten days be gone.’

‘Then lost it must be,’ said Gimli. ‘For what help is there to send thither, and how could it come there in time?’

‘I have no help to send, therefore I must go myself,’ said Aragorn. ‘But there is only one way through the mountains that will bring me to the coastlands before all is lost. That is the Paths of the Dead.’

_{The Lord of the Rings Book Five, Chapter 2: The Passing of the Grey Company
Page 780-1 (Houghton Mifflin Harcourt; Single Volume 50th Anniversary Edition)}

Arguably the result here is that Minas Tirith is saved. I consider this a good consequence of the decision to free Wormtongue.

Destruction in the Shire

Wormtongue certainly played a part in the destruction in the Shire. The one thing we know that Wormtongue did was to kill Lotho.

‘Then I will,’ said Saruman. ‘Worm killed your Chief, poor little fellow, your nice little Boss. Didn’t you, Worm? Stabbed him in his sleep, I believe. Buried him, I hope; though Worm has been very hungry lately. No, Worm is not really nice. You had better leave him to me.’

_{The Lord of the Rings Book Six, Chapter 8: The Scouring of the Shire
Page 1020 (Houghton Mifflin Harcourt; Single Volume 50th Anniversary Edition)}

Saruman was the architect of the destruction and would presumably have caused as much havoc if Wormtongue had not been there. We can assume that Lotho or some other hobbit would have died. I don't consider this a consequence of the decision to free Wormtongue

The death of Saruman

Leaving aside the metaphysical question of whether Saruman actually "died", it was certainly Wormtongue who removed him from Middle-earth. Frodo (who has presumably gained a lot of wisdom in these matters), did not want this to happen. When the hobbits want to kill Saruman after his attempt on Frodo's life, Frodo says:

‘No, Sam!’ said Frodo. ‘Do not kill him even now. For he has not hurt me. And in any case I do not wish him to be slain in this evil mood. He was great once, of a noble kind that we should not dare to raise our hands against. He is fallen, and his cure is beyond us; but I would still spare him, in the hope that he may find it.’

_{The Lord of the Rings Book Six, Chapter 8: The Scouring of the Shire
Page 1020 (Houghton Mifflin Harcourt; Single Volume 50th Anniversary Edition)}

Note that he is using a similar argument to the one Gandalf used about Wormtongue. I consider this neither a good nor bad consequence of the decision to free Wormtongue

Conclusion

I didn't judge any of those consequences to be bad, and one of them was actually good. So while Gandalf and Théoden understood that there might have been bad consequences, they freed Wormtongue as an act of mercy and were "rewarded" with a good outcome (as often happens in Tolkien's works when someone makes a moral choice).

Answer 2

No

Grima would've been in contact with Saruman during his time in Edoras. Saruman would've known of the hole under the wall and any other things before Wormtongue had even been released (This, however, is speculation).

But you, Wormtongue, you have done what you could for your true master. Some reward you have earned at least. Yet Saruman is apt to overlook his bargains. I should advise you to go quickly and remind him, lest he forget your faithful service.
_{The Lord of the Rings: The Two Towers, Chapter 6 - The Kind of the Golden Hall}

Seeming to imply that Gandalf was aware that Grima had been sending information back to Saruman.

Secondly as mentioned in the linked question's answer, the orcs in the books had found the culvert before they blew it up:

Orcs had crept... through the culvert... Then they sprang out.
Down from the wall leapt Gimli with a fierce cry that echoed in the cliffs. ‘Khazâd! Khazâd!’ He soon had work enough.
‘Ai-oi!’ he shouted. ‘The Orcs are behind the wall. Ai-oi! Come, Legolas! There are enough for us both. Khazâd ai-mênu!’

Gamling the Old looked down from the Hornburg, hearing the great voice of the dwarf above all the tumult. ‘The Orcs are in the Deep!’ he cried. ‘Helm! Helm! Forth Helmingas!’ he shouted as he leaped down the stair from the Rock with many men of Westfold at his back.
Their onset was fierce and sudden, and the Orcs gave way before them. Ere long they were hemmed in in the narrows of the gorge, and all were slain or driven shrieking into the chasm of the Deep to fall before the guardians of the hidden caves.
‘We must stop this rat-hole,’ said Gamling. ‘Dwarves are said to be cunning folk with stone. Lend us your aid, master!’
They gathered such small boulders and broken stones as they could find to hand, and under Gimli's direction the Westfold-men blocked up the inner end of the culvert, until only a narrow outlet remained. Then the Deeping-stream, swollen by the rain, ... spread slowly in cold pools from cliff to cliff.
_{The Lord of the Rings: The Two Towers, Chapter 7 - Helm's Deep}

This seems to suggest that Grima's main threat was known regardless of the bomb, and as it was crucial to emptying the Deep, and was therefore, likely visible.

---

As for the reasoning for sparing Wormtongue, in my opinion, Aragorn and Theoden both listened to Gandalf and trusted his judgement.

He says of Gollum (although about death in general):

Deserves it! I daresay he does. Many that live deserve death. And some that die deserve life. Can you give it to them? Then do not be too eager to deal out death in judgement. For even the very wise cannot see all ends.
_{The Lord of the Rings: Fellowship of the Ring, Chapter 2 - Shadow of the Past}

Tolkien seems to suggest that life should not be cut short by violence, unless at great need. Other examples include; the sparing of Gollum by Bilbo, Frodo sparing Saruman, Faramir sparing Sam and Frodo and finally, Thranduil sparing the Dwarven company.