Basically it's not against the rules to be racist. Be racist all you want. You can technically say I am part of the KKK and I hate black people without fear of being banned. But start slinging racial slurs and you got trouble.
We can't possibly filter all racial slurs. It's impossible because many of them are perfectly acceptable words used in correct context.
The reason DC is largely ignored is because we found that it's impossible to moderate closely without being accused of bias or taking a side. The only time we swing the mod stick in this forum is when posts are reported.
Nothing has changed with Flop's announcement here. He's just reminding everybody of the rules as a courtesy because it has been a trending issue here in D.C.