Because we choose to.... There is only one hate group and it is made up of all of the militant, hostile people from very, very different point of views who choose to let their personal beliefs and expectations translate into meanness.
Athiesm vs. deism, pro-homosexual beliefs vs anti-homosexual beliefs, conservative vs. liberal, ultra environmentally friendly vs. status quo. Just because we identify with certain beliefs or viewpoints doesn't make us hateful... I have met haters and non-haters in every one of these categories.
So I repeat, there's only really one hate group - and all other differences accounted for - it is only made up of people who choose to hate.
We actually can be passionate without being hateful :)