I used to be opposed to hate crime laws. I thought them unnecessary, because violence and harassment are already crimes.
I changed my mind after learning of the 'gay panic' defence, in which a person might claim as a legal defence that they thought someone of the same sex was coming on to them, and that idea is so horrible they freaked out and killed the other person.
With hate crime laws in place it is no longer allowed to use such claims as a defence in court, even if the jury would buy it.
At least, that is how I understand it and the reason I now support such laws.