There's only a few occasions where I've seen someone with dreads and not thought they were an asshole. So, I would say, don't do it. No one looks good with dreads (in my opinion), except for very rare occurrences.
You're going down a dark and slippery slope here. The argument could be applied towards anyone, and it's the same argument I've heard racist and bigots used, but slightly modified.
It's funny because I know a guy who looks Jamaican with his dreads who is one of the most genuinely nice guys I know...Not that niceness is a virtue anyone cares about. This thread is funny.