Most people only care about themselves and people who are like them. On Facebook you can tell a lot about someone by the political pages they like. If somebody likes Human Rights Campaign, they must be gay. 95% of outspoken feminists are women. If somebody has a more obscure issue they support, there's a good chance they're connected to it. If someone says "punish the deed, not the breed" (which I agree with) they probably own a pitbull (which I don't). Disability rights advocates are usually disabled. If someone wants to end discrimination against a group, it's a good chance they're part of that group. Most "bleeding heart" liberals don't care unless you're not white, female, LGBT, disabled, not Christian, or don't speak English as a first language. They only care about other discrimination if it involves them. And like anyone else they hate a lot of people, such as fundamentalists, fat people, "rednecks", etc.
It gets even dumber when you got someone like me who's in every majority group. We turn into your classic bigots and it's the same impulse. Almost everyone who complains about "political correctness" is white. I had people on a message board get mad at me for being a Christian once, but I don't experience discrimination or persecution in real life. There's some hate crimes against white people but not a lot. I take male privilege with a grain of salt because the gender roles are so strict for us - men have to be assholes but women can be whoever they want. But women still get paid less than us and still get treated like second-class citizens, and men don't, plus I've never faced any discrimination from being male. There is no prejudice against straight people, but homophobia is rampant here. Other religions and ideologies do face discrimination, especially Wicca and Islam. As for the language barrier, if you want to piss off a hardcore conservative, greet them en español. There's a reason people like us are rarely "bleeding heart" liberals: we don't get anything out of it. A ton of us are libertarian tho. Also, we're ignorant of prejudice because we never experience it. But experiencing prejudice doesn't make people more tolerant. It only means they care about issues they're connected to.
In short, people suck and I'm better than most of them. But people don't suck completely. There's no reason to hate somebody if you didn't get to know them first.