How is racist whites going out and lynching a black man any worse than racist blacks goint out and lynching a white man ?
It isn't worse, and AFAIK, the law as written doesn't make any claim to that effect. If a white hipster moves into a poor black urban neighborhood, and a bunch of black teens beat the shit out of him and tell him "Your kind don't belong on this side of town", then they should -- they must -- be prosecuted under hate-crime legislation. Their lives should be destroyed; they should lose their youth, and a good chunk of their adulthood, to prison; they should be subject to the full power of the penal system.
And -- just to be clear -- the exact same thing should happen to white kids who beat up black newcomers. Racially motivated violence is a dagger thrust at the heart of a civil, egalitarian society; it endangers its very premises. So the point is to send a message to everyone who feels even the whisper of a temptation to pull this crap, and the message is: try it, and we will fucking wreck you.
Look, it's not a big secret that most people are reluctant to talk about the fact that a lot of black-on-white crime is racially motivated, or at least has a strong racial subtext. It wouldn't surprise me if police departments and DAs are reluctant to use hate crime laws against black perps for fear of touching off a shitstorm. (Not to mention that in some urban areas, a lot of the power brokers are black, not white.)
That said, it doesn't really have anything to do with hate-crime laws, which offer the same penalties regardless of the targeted race AFAIK. It'd be unconstitutional to write a law that said that white-on-black crime was "worse" than black-on-white crime, or vice versa. But as we all know, there are places in the US where people find every possible reason to excuse the behavior of black criminals, blaming everything they do on poverty or racism or whatever...
...and then, there are other places in the US where law-abiding, middle-class black citizens are openly threatened by the local authorities, and told that if they stick around after the sun goes down, their lives may be forfeit.
So maybe it all sort of balances out -- not that that means much to the victims of any of these crimes.