I would've sided with King and the Civil Rights movement back in the 1960's and he'd be siding with me now on marriage.
Perhaps you'd like to hear what Coretta Scott King has to say about the subject? Perhaps I'm wrong, but I reckon she knew more about what he'd think than you do...
Her and MLK disagreed about many an issue. Ask his niece Alvea. On this the left is on the wrong side of history. So come out of your freedom hating delusion.
You assume a rapid, effective, and permanent backlash against same-sex marriage. You cannot assume the direction of the arrow of history.