Have we passed the homogamy tipping point?

A tipping point is when a small step along a continuous path suddenly makes a big, irreversible difference in some outcome. Here’s one illustration (which I got here):

The little bits of action have been having a little impact, until suddenly one more little bit of action creates a big impact — the straw breaks the camels back. In real life these moments are very hard to predict, and even in retrospect it’s not so clear what did it.

Legal homogamous marriage is spreading in the U.S. (and the world). The restriction on marriage increasingly looks like a crude, irrational violation of equal rights. A growing share of the public sees no reason to object to gay and lesbian marriage.

This doesn’t follow a tipping-point pattern, at least not yet. But here is a case where 50% is potentially a tipping point rather than a mere milestone or watershed. That is because of 50%+1 winner-take all voting. And that’s why this week’s successful ballot measures in three states in favor of legal homogamous marriage– Maine, Maryland and Washington — are so important.

But the tipping point actually may have preceded them, when marriage rights broke out of New England, in Washington, D.C. in 2010, by a city council vote. (Iowa went earlier by court order.)

When New York followed DC by legislative action in 2011, the percentage of the population in marriage-equality states more than doubled, from 5% to 11%. Even without the judicial branch, which will do something in the next year or so, the trajectory here is steeply upward.

In a truly Rovian moment of prognostication, Brian Brown from the National Organization for Marriage gave this analysis earlier this year:

Proponents of same-sex marriage have created a myth of inevitability, and folks in the polling world have used language that has often helped them… The only poll that counts is the voters, and if you look at that, we’ve won every single one. If you look at trend lines, the trend lines are in our direction.

And that makes sense (that is, the opposite of what Brown said): if we’ve shifted to a majority, or close to it, nationally, then plenty of states and local areas are well beyond 50%, and that’s enough for ballot measures where they are permitted.

As a result of social movement action, legal challenges, changing attitudes, and cohort replacement, marriage equality appears to be spreading, like a forest fire or disease epidemic — only better.