That attitude is what creates white supremecists because forced inferiority creates animocity in the individual not the race. A lot of black people don't like whites because of our history of treating them like children or worse.
Through white guilt of that, we create a similar situation thats more subtle and is the undercurrent of most racism in current society.
By saying "only blacks can be racist" you are coddling them like children, while "whites can't be racist"....because why? Because they should know better. THat is the underlying mentality of white people who are racist but dont realize it. That subtle idea that blacks have some sort of leeway because they are vaguely inferior in terms of societal intelligence.
Which isn't true, but many black people seem to embrace that, simply because it gives them a false sense of power.
my .02
I'm not racist, I just don't believe in white guilt either.
ps- im drunk
pps- previous statement is not universal by any means but I see examples of it everywhere (see: the news)