A generation from now, we'll look back in bewilderment that anyone could possibly care whether a gay couple wants to get married or not,
I'd say he's right. Here's a graph I produced recently from data from the 2004 American National Election Study.

Some people like to claim that young people just support it because they don't know any better yet. But that wouldn't explain why my cohort--low 40s--is more accepting than my mom's cohort (late 70s). It's pretty clear, a multi-generational shift is occuring. I predict same-sex marriage is here to stay in Massachusetts, and will exist in several more states before I retire.