That's because they seek to impose conformity of thought on other people. This, in turn, is because they are extremely unhappy... and believe their unhappiness results from the thoughts of other people.
They believe that only by changing the thought patterns of their friends, neighbors and family members can they become happy.
Which is why they make a perfect “victim” group for leftists and democrats, i.e. believers in so-called “positive rights” which are no true rights at all. If one needs the absolute affirmation of everyone else around him, he is putting demands and obligations upon others that take away their negative rights which are the only true rights there are.
http://www.youtube.com/watch?v=gXOEkj6Jz44
If homosexuals truly believed what they were doing was right then they wouldn’t care what anyone else thought of them.