Here's something interesting

John Judis argues--persuasively--that social liberals need not worry about the new pro-life polls because people become more socially conservative during economically lean times. Money quote:

I would also make two other points. The first is that the tilt toward pro-life sentiment doesn't necessarily imply a changed view of whether the Supreme Court should overturn Roe v. Wade. In fact, a recent CNN poll shows that Americans, by 68 to 30 percent, do not want to overturn it; the Gallup and Pew polls are thus gauging personal sentiment, not policy preferences. Americans can be expected to embrace a more conservative social ideology during this period without endorsing conservative social policies.

The second point I'd make is that, though people become personally more conservative during economic downturns, they also seem less likely during those downturns to base their support for public officials and candidates on social issues like abortion or gun rights. In the 1920s, politicians battled over prohibition; in the 1930s, there was no equivalent social issue. Americans were worried about the economy and about being drawn into a new world war.

This doesn't quite explain why gay rights seem to have been picking up momentum, though there might not be a grand unified theory for this sort of thing.