I didn't go into it but there are a lot of ways that expression hatred helps the situation:
1) Hatred bottled up eventually comes out either as violence or speech. I'd rather it be expressed via speech.
2) When people express their real feelings, that can serve as a warning to the rest of us. If I know you hate white men, I'll know to steer clear.
3) When people express feelings that are illogical, we become aware of their misconception and are given the chance to help them get a more nuanced and accurate understanding of a situation.
4) Sometimes we are wrong and they are right, which is ia general argument in favor of speech that is classified as disinformation. In these cases which we absolutely cannot determine apriori, the ONLY way we can be corrected is if we allow people to correct us by allowing them to speak.

I'm just scratching the surface here. John Stewart Mill does a pretty good job explaining all the ins and outs in "On Liberty"