I think that everyone is conservative to the degree that they don't wish their own lives altered by someone else and progressive to the degree that they wish to inflict their own practices on others by coercion. That's sort of a sad definition of "progressive" but it seems accurate enough these days.
As far as nature vs. nurture with regard to human sexual behavior, I'd say the jury is pretty much still out on that one. Maybe both. I really couldn't give an intelligent opinion on it.
Oh, well, you beat me to it. LOL!