OP I agree with you entirely, although I expect there will be some denial of that. In the past few weeks the amount of threads Ive seen dissing black women are disgusting, from nasty insinuations about black women's mental health issues not really mattering, to complete tearing down of black female singers. I don't bother to say much about it because someone will always come along "oh but it happens to other women too" well yes it does at times, but when there is a pattern/succession and its the same kind of reasons, its glaringly obvious. I hate people aiming to tell me what is racist and what isn't, via their definition that has nothing to do with my own race and culture.
There's also the regularlity of the golliwog threads that just have to come up so often, and the amount of posters who pretend theyve always had a golliwog, it was their favourite toy of childhood, oh its not a caricature of a black person, why are black people offended..and my favourite, which always lands somewhere in the thread "my dad is black as the ace of spades and HE'S not offended!". Oh so thats ok then 
Im glad sexism is stamped on immediately. I hate any form of sexism. On the other hand casual racism seems to be just fine and its disappointing. I couldnt give much of a shit about racists I just find them stupid and dont really engage in the threads anymore..you cant talk to a thick impenetrable wall of a person and get any sense out of them. But it does surprise me still..for some reason I thought MN would be different to various sites out there. It still makes me smile when I see people describe something as being "like something out of the Daily Mail" then on another thread theyre spouting nonsense about black people.
When I 1st joined I had a baptism of fire
there'd been a programme on the night before, Im sure it was Undateables..ages ago when series 1st started, and a black man was naked in one scene. Next day, cue loads of comments and jokes about a black man's cock. OK I can take a joke like anybody else. But it began to go too far in terms of all a black man is good for, comparisons etc. When I pointed out hang on this is too much bordering on racist stereotypes I was called "professionally offended" by loads of posters, then told I was being reported. Wtf..can you imagine if id started a thread about white mens cocks and then black posters started commenting in derogatory fashion?! But.. the poster who backed me on that thread was a lovely woman - not black, my point on that being you don't have to be black to try to understand or empathise with racism. You know right from wrong.
There are a good few people who challenge racism on here though, I cant deny that.. but they tend to get drowned out. & when its a well thought out response from posters who are fairminded, that response is inevitably completely ignored. Especially by the my dad/sis in law/mate/next door neighbour's cat is black crew.
I think we are slightly overdue for a golliwog thread. In this forum of "racism? what racism? Ive never seen anything Nope, nothing at all". Another month or so should do it I think. Stick "golliwog" in the search box and see how many times various people have actually felt a need to create a thread on it again under the wide eyed pretence of "but I just dont KNOW why black people find golliwogs offensive - do all of you?" and tell me there arent some seriously stupid people around here... if we heard of kids doing that kind of thing there'd be plenty said, but it seems when adults do it, its nothing really