I don't believe in stereotypes in the sense that every person is unique so the fact that a person belongs to one group does not mean that he or she will fit all of the stereotypes of that particular group.
That said though, stereotypes did come from somewhere. They didn't just appear out of thin air, and though stereotypes morph people into caricatures of their particular minority, that isn't to say that they're completely without merit. I do believe that everybody fits at least some of the stereotypes of their particular group, and if they say don't it's because they're suppressing it out of insecurity.
I, for instance, am gay. I don't fit most of the stereotypes that make up a gay person, but there are some that I definitely do. And I have no doubt that if I were a straight guy, some of those things would be different.