I had early-voted agin' our famous Amendment. It ended up passing 61-39, which is pretty vast. You can't overcome that sort of gap by comfortably thinking to yourself "well, they didn't know what it meant" or "we'll reverse that in 4 years."
At the same time, my own region was the only significant region to vote against, along with the counties that have major college presences. The single most statistically relevant factor in predicting how a person voted on the amendment was level of education - more than age, more than party, more than religious preference.
I don't correlate education with intelligence, necessarily. I correlate it with experience of worldviews beyond your own, and with mixing with all types of people. There were no "gay people" at my high school in the early 90s (like there are no gay people in Iran), and I went to high school in a relatively progressive community. Now there are plenty of gay people there and it's no big deal. I bet there are "zero" gay people in a lot of the towns that voted overwhelmingly for the amendment.
I'm convinced, based on demographic trends, that we will all get there eventually. Although Alabama just took its anti-miscegenation law off the books in the 2000s.