Racism is supposed to be against the rules, but some people get away with it.
I seriously don't know why racist jokes are tolerated. I remember there were occasions where people get banned for saying "nigger" before I was a mod. I never believe in "race", and I never tolerate racism. The rules, as put up by Daniel, never stated only racist jokes are allowed. I don't think it'll be pleasant if people constantly put up racial slurs and imply it as a "joke." The boards wouldn't look so friendly in the long run.
I've been here longer than you and don't know anyone that was banned simply for the use of the word nigger. Real racism is not tolerated, racist jokes kept to a joke thread are no worse than misogyny, the use of puns, dead baby jokes, sexual jokes, or truthfully any other form of humor used by adults. Jokes are a means of bringing taboo subjects to the light of day and allowing open discussion of them. If you can not joke on a subject you can not easily talk about something in a reasoned manner.
Any subject that can not be openly joked about will instantly bring about knee jerk reactions in a debate and keep the debate purely emotional.
Actual racism has no place in the forums hence althalus being repeatedly banned.