A brief history of how we got here

This excellent article in the Atlantic tells the whole story, starting with a man named Baker....

When Wolfson was a law student at Harvard in 1983, his adviser tried to discourage him from writing his thesis on gay marriage, on the grounds that it was too far-fetched. Sullivan’s 1989 New Republic essay, “Here Comes the Groom,” got a similar reception. “It was difficult just to get past the laugh factor at the beginning,” Sullivan recalled. “I remember going on Crossfire in the early days and having Gary Bauer laugh in my face—‘It’s the most bizarre and silly idea to come down the pike in a long time! It’s ludicrous!’”

and then, how the message changed after the cluster of the Prop8 campaign, as the participating groups started to strategize together

There was stiff resistance within the movement to the new approach. Some thought it made no sense or wasn’t aggressive enough; some resented the strictly vetted, disciplined, sanitized faces the movement was putting forth. But in 2012, after 31 straight losses for gay marriage at the ballot box, Freedom to Marry spearheaded a centralized, politically savvy, message-tested campaign in four states—Maine, Maryland, Minnesota, and Washington. On Election Day, the gay-marriage side won in all four states.