I was about to disagree with you, but you explained your point rather nicely at the end there.
Yes I agree there is a difference between just being a plain arse and being politically incorrect, one is done out of pure igrorance and is actually hate directed, the latter is done to either make a point about society or for comic appeal, where the society point should be poinient and the joke should be just funny so people can laugh and it's obvious you don't actually mean offence.
The thing I am going to have to make a point about is when someone is just says a joke which isn't really directed at the group the people take offense to. People who say people are being PC is when a group has found offense in something that wasn't really offensive.
In the RE5 case or in the l4d2 case (shooting black people was being racist, was the point and thus all black zombies should be taken out). Capcom and valve obviously wern't or even trying to be offensive, they were set in Africa and New Orleans (where there is a sizable population of black people), and thus it stands to reason people there would be black. Extremist anti racism groups stated that this was being offensive and racist to black people, and attempted to censor it for being politically incorrect, when in fact it wasn't, as I'm sure all of us have the sense to work out.
The people who get annoyed at Political correctness usually have a point, and it's when something that shouldn't be censored is censored, such as when the people in charge decide that something is offensive when no one is actually offended by it, or if they are they need to grow up and realise that having black zombies isn't offensive to anyone. Nothing HAPPENS when you're offended, it's not a case of "there was a black zombie, I shot it and when I woke up..I had lepracy!" (bonus points if you get where that came from

). It also comes from shoehorning things into it just to be politically correct for the sake of it.
I still don't like the idea of a norse god being black, not because I don't like black people but because he wasnt black in the comics or ANY of the norse mythology, which even though they are both fiction, still have their lore specifically outlined.
If we took an black god, and made him white because we feel like it, there would be a FUCKING MASSIVE outcry of racism, yet when we make white characters black, it's okay because we're being politically correct or diverse. I would be just as annoyed if they had Blade played by a white guy, as I am the norse god being played by a black guy. Blade is black and awesome, Norse gods are white and have fucking massive beards and come from a land of WHITE people. Their gods are going to be white, as outlined by years of mythology and dogma.
If we made a movie using christian mythology and changed the nationality and race of characters, there would be an uproar about it from the Christians, because even if I don't believe in it, the source material outlines how these characters should be.
Its the double standards that make people annoyed, if a joke is aimed at the majority it's okay, but if it's a minority (be it gays, muslims, blacks, or anything in between), someone, somewhere MIGHT take offense to it and it's rendered politically incorrect and censorable. Not everyone is a racist hate mongerer, most people just want to make people laugh, or make a game with black people in it because it's set in africa. Don't make everyone else suffer because a few select people hate everyone else, make them suffer.
Making a law about offending people is totally bollocks anyway, what offends me might not offend you, it all comes to gether about how you're raised, how tolerant you are, your culture and beliefs and anything else that makes you, YOU. The people who get riled up and make a big issue out of anything they can get their hands on don't deserve anyones attention, because THEY are the people who want everyone to hate each other, by making it appear wrong to say X.
If I say "don't do that I might catch the gay" I will blatently say it in a light hearted way because everyone knows you can't catch the gay, and I have nothing against gay people at all. Yet some bigwig would class that politically incorrect and attempt to censor me, because one gay person MIGHT be offended by me saying that, which means that if a gay person does get offended by me, it would mean they're not secure in their self and they're the ones that needs to sort it out, not me with my light hearted joke.
If someone makes a joke about Geeks, I will laugh, because I don't care, I'm comfortable with the way I am, and everybody else should be comfortable with who they are. Nobody likes anyone that is genuinely racist, sexist or homophobic, because they're utter cunts, which should make you feel even more secure about who you are, because prejudice people are generally booted out of social circles because more often than not people will just see them as cunts.
TL DR:
It's okay to shoot a white zombie, but shoot a black zombie and you will have hell to pay for being a KKK/Hitler spawn of satan.
Yahtzee got it right:
"A society where anyone can make jokes about anyone else and everyone laughs is a truly tolerant society. Political correctness-charged censorship only serves to engender resentment and distance between social groups. "