#3 explains the problem perfectly.  They tend to think they know what's best for everyone.

Let me ask you.....I happen to believe in God.  Do I need to attend the same church as you do (by that, I mean denomination, not building)....or ANY church, for that matter, in order for that to be valid?  I think gays should be able to get married.  Is my belief in God not valid because I hold that view?