In Deathly Hallows, why did they have to wear Slytherin's locket?

Question

Obviously, heavy spoilers for Harry Potter and the Deathly Hallows, do not read if you don't want to be spoiled.

So they find the locket horcrux, and before they figure out how to destroy it, they decide to take turns wearing it. Why on Earth would they do that?
We know (and they quickly figure out) what influence it can have on one's mood, and it eventually leads Ron to give up and abandon Harry and Hermione. Hermione, on the other hand, has a wonderful bag that can take whatever you put in it. Why not just put the Horcrux in the bag? Do we have any information in canon that indicates the Horcrux would have still had such an impact on Hermione's mind?

It seems a pretty suicidal behavior to me to wear a Horcrux which basically makes you weaker, especially if you're on a path to destroy such Horcrux.

ETA
While there are good answers, I feel like I cannot accept one of them yet due to Anthony Grist's first comment to this answer which seem very relevant:
The main thing that bothered me about the whole thing is that Harry has an entirely secure bag hanging around his neck at that point. There's no way he could have forgotten about it since it would have been right there when he hung the locket around his neck too.

Answer 1

In universe:

Harry (and later when Hermione and Ron took their turns) put it on because that was the safest place to keep it. As Harry said (page 276 of Scholastic paperback):

"Keep it safe till we work out how to destroy it," Harry replied, and, little though he wanted to, he hung the chain around his own neck,"

My guess is that Harry felt that keeping it anywhere else, even in Hermione's bag, was too big a risk. Keeping it around one of their necks meant that any situation that needed running or apparating would keep the locket with one of them and not left at the campsite, etc.

Out of universe:

JK Rowling probably needed it to negatively affect Harry, and then Ron, during the trio's journey.

Answer 2

Well, they wouldn't be able to use Hermiones bag due to the Horcruxes being protected from the Accio command, as just reaching in for small items was proved to be impossible (When harry was looking for the potion).

It also would remove a large chunk of "plot" as it doesn't make for very good storytelling if they just shove the necklace of douche-baggery in a handy compartment. It adds to the drama and changes the dynamic of the group.

Also they did not want to lose it, so the logical answer for them was to wear it.

Answer 3

They didn't want to leave it lying around, in case it got lost or stolen.

‘Hm,’ said Hermione, looking down at the heavy locket. ‘Well, maybe we ought not to wear it. We can just keep it in the tent.’

‘We are not leaving that Horcrux lying around,’ Harry stated firmly. ‘If we lose it, if it gets stolen –’

‘Oh, all right, all right,’ said Hermione, and she placed it around her own neck and tucked it out of sight down the front of her shirt. ‘But we’ll take turns wearing it, so nobody keeps it on too long.’

‘Great,’ said Ron irritably, ‘and now we’ve sorted that out, can we please get some food?’

_{^{HP - Deathly Hallows. Chapter 15: The Goblin’s Revenge}}

You may wish to note that despite a wide array of extremely potent and clever spells being used, Harry and crew are able to locate the hidden Horcruxes with relative ease, with the final Horcrux (Nagini) being the hardest to destroy simply because it's with Voldemort at all times.

Answer 4

The logic of not putting the locket in the bag (plot points aside) is that the bag and thus everything in it could be lost or stolen, which would increase the probability of the locket being lost as well.

Actually wearing the locket minimizes that potential and ensures that they are constantly aware of its location. If it were in the bag there would be an air of uncertainty, though the assumption would be that it is secure. Finally, if for any reason they had to abandon their belongings, as in they were separated from them and couldn't go back, they would still have the locket.

Answer 5

The locket was capable of influencing its wearer's thoughts, making them paranoid and possessive. It was able to influence people to a lesser extent even when they weren't wearing it, as shown when Ron attempts to destroy it. It's likely that the locket clouded their judgement and prevented them from realizing they could keep it someplace other than around their necks.

Answer 6

Honestly, Harry was wearing a huge, secure rucksack that he could but the locket in. On the other hand, He might think it could get lost in 'Hermione Granger's' beaded bag since in the book it said: "She gave the fragile-looking bag a little shake and it echoed like a cargo hold as a number of heavy objects rolled around inside it."

Answer 7

I think the horcruxes are immune to the accio spell, because it's an obvious one to use if you are looking for a horcrux, ie, just go somewhere and yell accio horcrux. It would be ridiculously easy then to find it. When Harry tries to recover the goblet in the vault, he yells accio to the goblet but it did not work. Also to the sword in the lake. This spell makes it just too easy to acquire things of immense value. So I do not believe they would have been able to access the locket from the bag with an accio type spell.