I think part of it is... Well, as Nenya said, it's about intent.

To take a far less extreme example than beating someone to death with a golf club:

Spray painting graffiti all over a wall is, technically, a crime. But it's, like, 'mischief'. It's not a *big* crime. Spray painting your tag on a random wall is no big deal.

Spray painting, say, 'fags suck' on a random wall is dumb.

Spray painting 'fags suck' specifically on the wall of the house of your neighbourhood lesbians, however, is about more than just 'airing your grievances' to the world at large. That kind of thing is done, specifically, to threaten/intimidate a particular person (or group there-of).

If you have hate-crime legislation in place, the lesbians and their lawyer can point out that the 'fags suck' slogan was clearly meant to intimidate the people living in the house, and have that statement backed up by law.
Whereas, if there is no such legislation, then the representation of the spray-painters can (theoretically) get them off with something like:
"It was just a little graffiti. You're over-reacting. If they'd actually meant to intimidate these women and their 'lifestyle', wouldn't they have, like, ganged up on them in a parking lot or something?"
The intent of the crime could be easily overlooked (on purpose or not) by the judge simply because there's nothing on the law books that says they have to pay more attention to it than that.

Y'know? :-)

So that's how it helps. I think. ;-)