Why are people so hostile about other's music choices?

My favorite bands are Green Day and Sum 41 and everyone's like that's gay music, that's not punk, why don't you listen to something that doesn't suck? Is it that hard to see that there are many kinds of music because people have varied tastes in music? I personally am sick of hearing "black and yellow, black and yellow, black and yellow" blaring through the hall in my dorm but I don't attack people about it. Am I the only one that thinks you should just listen to what you like because it is what you like, not because other people think its cool?