Gay Marriage Is Not the "New Abortion"
This WaPost article reports a common analogy:
Activists on both sides have begun to speak of the issue as "the new abortion" -- a passionate and uncompromising struggle that will be fought in Congress, the courts and state legislatures, and through referendums for at least a decade to come.
The comparison doesn't hold in one, very important respect: Abortions are sad. Weddings are happy. Having an abortion--or having a friend or relative who has one--may make you more supportive of abortion rights, but it won't make you celebrate the idea. Abortion won't make you smile.
People support abortion rights out of fear. They support gay marriage out of love. There are, of course, non-emotional arguments on both sides of both issues, but the fundamental feelings are different. That changes the politics, particularly with time and experience.