Why did Hermione warn Umbridge not to insult the centaurs?

Question

In The Order Of The Phoenix, Hermione takes Umbridge into the forest in order to get rid of her:

We only came in here because we hoped you'd drive her off for us! - Hermione

Yet when Umbridge insults the Centaurs by calling them 'half-breeds', she tries to stop her:

Thatʹs right!ʹ said Umbridge, in an even higher voice, ʹso be very careful! By the laws laid down by the Department for the Regulation and Control of Magical Creatures, any attack by half‐breeds such as yourselves on a human ‐ʹ
ʹWhat did you call us?ʹ shouted a wild‐looking black centaur, whom Harry recognised as Bane. There was a great deal of angry muttering and tightening of bowstrings around them.
ʹDonʹt call them that!ʹ Hermione said furiously

And again -

ʹFilthy half‐breeds!ʹ she screamed, her hands still tight over her head. ʹBeasts! Uncontrolled animals!ʹ
ʹBe quiet!ʹ shouted Hermione

Since her aim was for Umbridge to insult the Centaurs enough for them to take her away, why did Hermione try and stop Umbridge insulting them?

Answer 1

Hermione probably emotionally reacted to Umbridge’s prejudice.

Hermione most likely reacted on an instinctively emotional level once she heard Umbridge insult the centaurs, despite her plan being for them to chase Umbridge away. She very much hates any human-like creatures being treated badly, and this can sometimes override her good sense and logic. For example, when she learned there were house-elves working in the kitchens, she refused to eat her food. Despite that whether one girl ate her dinner or not wouldn't affect the welfare of the house-elves, and that she’d had no other way to get food at Hogwarts, she decided not to eat.

“Hermione looked down at her hardly touched plate of food, then put her knife and fork down upon it and pushed it away from her.

‘Oh, c’mon, ’Er-my-knee,’ said Ron, accidentally spraying Harry with bits of Yorkshire pudding. ‘Oops – sorry, ’Arry –’ He swallowed. ‘You won’t get them sick leave by starving yourself!’

‘Slave labour,’ said Hermione, breathing hard through her nose. ‘That’s what made this dinner. Slave labour.’

And she refused to eat another bite.”
_{^{- Harry Potter and the Goblet of Fire, Chapter 12 (The Triwizard Tournament)}}

This wasn’t a very well thought out choice, and she goes back to eating the food that the house-elves cook when she gets hungry enough, despite her initial protests.

“You’re eating again, I notice,’ said Ron, watching Hermione add liberal amounts of jam to her buttered toast.

‘I’ve decided there are better ways of making a stand about elf rights,’ said Hermione haughtily.

‘Yeah … and you were hungry,’ said Ron, grinning.”
_{^{- Harry Potter and the Goblet of Fire, Chapter 13 (Mad-Eye Moody)}}

However, her instinctive reaction was to do something that didn’t actually make sense in the situation. While in this case, it’s theoretically possible that her reactions were meant to distance her and Harry from Umbridge’s way of thinking, knowing her, it’s more likely an emotional response.

Answer 2

I believe Hermione had not thought of Umbridge's non-human bigotry when she led her into the forest. She was thinking only of the previous exchange she had witnessed between Hagrid and the centaurs earlier in Order of the Phoenix (chapter thirty, "Grawp"):

"As are you, human," said Bane, "coming back to our forest when we warned you --"

"Now listen ter me," said Hagrid angrily. "I'll have less of the 'our' forest, if it's all the same ter you. It's not up to you who comes and goes in here --"

"No more is it up to you, Hagrid," said Magorian smoothly. "I shall let you pass today because you are accompanied by your young --"

"They're not his!" interrupted Bane contemptuously. "Students, Magorian, from up at the school! They probably have already profited from the traitor Firenze's teachings..."

"Nevertheless," said Magorian calmly, "the slaughter of foals is a terrible crime...We do not touch the innocent. Today, Hagrid, you pass. Henceforth, stay away from this place."

Furthermore, from later comments, they took this exchange to mean the centaurs wanted no humans in their forest:

"Hagrid," said Hermione breathlessly, skirting the patch of nettles they had passed on their way there, "if the centaurs don't want humans in the forest, it doesn't really look as though Harry and I will be able --"

Therefore, I have always believed the explanation of the scene of Umbridge confronting the centaurs to be that Hermione had not given complete thought to what would happen when Umbridge met the centaurs. Her goal was only that the centaurs would try to chase Umbridge off for being an adult human in the forest, while they had already said they won't harm children. She was then shocked, especially due to her identity as a non-human rights activist, when Umbridge started insulting them to their faces, and wanted to defend them.

And if you think about it, Hermione would have been not a very good non-human ally, indeed, if her first thought had been to bring a racist to the centaurs' forest so that she would hurl epithets at them. Although, as the centaurs pointed out, Hermione was still guilty of the lesser offense of intending to use them, however harmlessly, to achieve her own ends.

Answer 3

This is conjecture, but it could be that Hermione wanted Umbridge to be scared off but not killed. I don't believe Hermione ever kills in the series.

The plan is risky enough, for both the students and Umbridge, but they are desperate. All they need to do is for the centaurs to occupy Umbridge long enough for them to get away. Hermione probably didn't count on Umbridge being stupid enough to insult a herd of angry centaurs to their faces. That is stupid enough to get them all killed. So she is saying be quiet to Umbridge to stop the situation being escalated further.

Answer 4

Other than spontaneous emotional impulse and she not wanting to fatally harm Umbridge, there's a big possibility that it was Hermione's tactical move.

Hermione knew very well that Centaurs were going to attack. But, she wasn't sure if they would attack only Umbridge or other humans with her, too. By countering Umbridge, Hermione proved to the herd that the insult wasn't a group action.