Big Bad Racist Bastard

I hate how when someone says something racists (or potentially racist) to a Caucasian or white person, it doesn't mean a thing. However, the second you say something back you're the big bad racist bastard.

Example:
"So this guy messages me right 'hey sexc wanna watch me get hard on cam' as it happens he's black.. so I tell him off right. I didn't say anything racial and he comes back with 'Fuck off you white trash hoe. I bet you blow horses for quarters'. So obviously I replied back with something racial and that makes ME the racist, just because I'm white"

This is a real message that I received alongside an idea to do a rant on this topic. Which I must agree should have been done by now.

I know for one that I've been in the same situation a couple of times, and have been given shit for it even though I wasn't the one to begin it.
So why is it? How come we get the shit end of the stick when it comes to racism? Are you still sore that we took your land and made it more useful and productive?

Well fuck your shit. I'm not one to purposely be offensive with racism but if you say something racist to me you can sure as hell bet that I'm going to come right back at you.

I would like to be enlightened though, why is it that we're automatically more racist and are treated harsher for being racist, then those of other races who discriminate just as much as us?
Comment with your answer.