Why is gay marriage inevitable? First, the basic insight of the gay rights movement over the last four decades has proved powerfully correct: As more gays and lesbians have come out of the closet, the social environment has become more gay friendly. In turn, as the social environment has become more hospitable, more gays and lesbians have felt free to come out of the closet. This social dynamic is powerfully reinforcing and unlikely to be reversed.

One factor that most strongly predicts support for gay equality is knowing someone who is gay. As more gays and lesbians come out of the closet, more parents, children, siblings, friends, neighbors and co-workers know or love someone who is gay. Because few people favor discrimination against those they know and love, every gay person coming out of the closet creates more supporters of gay equality.

The number of Americans reporting that they know somebody who is openly gay tripled between 1985 and 2000, reaching 75%. One study in 2004 found that among those who reported knowing someone who is gay, 65% favored either gay marriage or civil unions, while only 35% of those who reported not knowing any gay people supported them.

A second reason that gay marriage seems inevitable is that young people so strongly support it.