I think the 'fear' itself comes from the development of our society. No one group or person is to blame except the persons who commit violent acts against people who are just being themselves.
The definition of marriage is where everyone has their problem. If we consider the Christian side of things, which is where you'll find most of the debate on the against side for marriage. Then again, we have a very musculine society and most people feel threatened for some reason if a guy is attracted to them. Like it's going to turn them into a raging flashly shirt sporting homo.
Acceptance is all one can do. You don't have to like it, you just have to understand this is how people are and accept them for it.
In my opinion gay marriage isn't ontop of most gays agenda, but those who want to should be able to share the same legal rights as a married couple.