I'm not gonna comment on the psychological aspect of gay marriage; I don't know diddly about that.
But as for the political aspect of it, this is just one more nail in Bush's political coffin. Once again, he's alienating everyone else just to get in tight with his ultra-conservative supporters. 60% or so of all Americans may not support gay marriage, but ask people whether they want a constitutional ban on it and close to 70% of all Americans will say NO. Two thirds of all the state legislative houses in the USA have to ratify it before it could go on the books. With those sorts of requirements and the number of people ambivalent about the proposed amendment, this amendment is NEVER going to get ratified.
I think Bush knows this. He's trying to use gay marriage as a wedge issue to split the Democrats. But this could VERY easily backfire on him because there are a lot of Republicans who won't support the proposed amendment. Lots of states' rights Republicans are dismayed that Bush is trying to rewrite the Constitution on an issue that they think should be left to the states. And the Log Cabin Republicans, a Republican gay-rights group, has already publicly announced that they are going to oppose Bush on the gay marriage amendment.
(I never understood what the Log Cabin Republicans were all about. I mean, they're in favor of gay rights, but they vote Republican? Cripes, what the hell are they thinking?)
Bush is already splitting his own party over this issue. If the Republican moderates are smart enough, they'll stay home in November because Dubya has been a disaster for eveything (environment, gay-rights, civil liberties) that they stand for. If they really get smart (not likely, but one can always hope), they'll vote for the Democrat nominee to send a message to the Republican right wing.
People are expecting a close race in November. I am too, but every time I see Bush run right instead of to the center, I can't help but think that his message of being a "compassionate conservative" is going to fall flat. One of the reasons Bush "won" in 2000 was that he managed to deceive people into thinking that he was a moderate Republican. After today (and after everything else that has happened in the last three years), he's going to have a MUCH tougher time of doing that.
No moderate Republican with half a brain should vote for Bush in November.