It's not a cancer. It's just sometimes taken too far. Everything has a bad side or a weakness. To be described as a "cancer" your labeling it as purely bad. It's not.
The encouragement to use language sensitive to prejudice. There is a heap of oversensitivity there but there are words like "faggot" and so on that do make sense.
Getting a bit sidetracked, but I find 'political correctness' to be a catch-all term used for several things. One is in actual politics and public statements and so on where such language is obviously not appropriate. On a personal level, bigoted people are going to be bigoted regardless of how politically correct things are portrayed. In terms of art, there's a distinction between using sensitive or 'politically incorrect' subject matter for a reason, as opposed to just being abusive and offensive. I don't think people should shy away from 'difficult' topics because they may be deemed controversial or politically incorrect.
Well, it depends on the impact of what they do. It always does. And it's not really about topics, it's about specific messages.
But that's the thing. It may not be your intention, but your summoning the ghost of homophobia. That word goes back to homosexual burnings. And to use a gay associated word as an insult generally kind of implies that gays are bad.