If cause-and-effect, there should be some effect

I wrote a couple days ago about David Blankenhorn's lukewarm agreement that, yeah, marriage for gays is probably a good idea. Here's a bit more about it. As part of his New York Times editorial Blankenhorn wrote:

I had also hoped that debating gay marriage might help to lead heterosexual America to a broader and more positive recommitment to marriage as an institution. But it hasn’t happened.
…
[I]f fighting gay marriage was going to help marriage overall, I think we’d have seen some signs of it by now.