So ... what? You want people to be arrested if they think that? Prison? Fined? Expand upon this more, please.
It's impossible (and the things that would make it possible are pretty immoral) to arrest someone because of what they think, but if someone goes on Twitter, for example, and writes "I hate Obama because he's black" (that's a grotesque simplification, but you get the point), that person should, at least, be fined.