Here's the thing...in writing you will never be able to please everyone who reads your book. Because you do not know who your audience is going to consist of and there is no way to predict what is going to offend them or not. Also, shouldn't we, as writers, have the freedom to write whatever we want? If I want to write a character who is a racist shouldn't I be able to do that? Shouldn't I be able to have him say the most terrible, ugly, racist slurs without being labelled a racist myself? I am not my characters - I am me - the writer - we are not one and the same. If my story demands a racist or a Nazi or any other disturbing character should I not have the freedom to bring them to life in all their flawed majesty?
Don't censor me. I should be able to write what I want - as long as it is not illegal. And it is not illegal to write a racist character or call another character disabled or anything else that might fall into the category of politically incorrect. The only thing I would tell writers NOT to do is to defame someone or an organisation in writing: do not bitch about your boss or workplace, or your cranky uncle or aunt, or that bitch in school who made your life hell. You can't do that. You can't paint real people as dicks in fiction. You can't use their names or their likeness or anything else associated with them.
Back to being politically correct...there's freedom of speech and writers just being plain dumb. We should be able to write what we want but be cautious: if your entire plot and characters comes across as racist propaganda you might turn the entire internet against you and become the target of trolls, facebook hate pages, and numerous rants on YouTube.
Should you be politically correct? To a degree, yes. Ask yourself: will my book offend people of this religion? or people of this race? If you think it might come across as massively offensive perhaps tone it back a tad....you don't want to spend the rest of your life getting prank phone calls and pizzas delivered to your house!