This graph charts the change in overall view of gay rights in the US. As Andrew Sullivan notes, something happened around 1990 that accelerated the approval of gay relationships. He takes a fair bit of credit for it, for which theory YMMV. But I think he does have a point that the changes from being an outcast defiant counter-culture, to demanding to be part of the dominant culture, has something to do with it. Frankly, we started coming out, and most of us are pretty average folks. We are sons and daughters, fathers and mothers, friends and relatives. And we aren't scary at all.
When combined with other data we've reviewed on states views on a variety of issues as well as on the rate of change on the marriage issue state by state, we can see that in some states, it's approaching a non-issue. But still, over 50% in the "always wrong" category does not bode well for change at a national level anytime soon.