Americans have a deep seated problem with gay people; don't know why, don't care, it's stupid and sad, but true.
Some Americans have a deep seated problem with gay people, and they are the minority now. Hell, given how most of the world acts towards gay people, the USA would still be at the higher end of acceptance even if that were true. Try being openly gay in parts of the Middle East that aren't Israel or parts of Africa that aren't South Africa. See how long you stay alive, much less accepted.
Take a look at your own poll results. Only recently have the numbers for agreement with gay marriage gone up past 50%. That's still
really bad. If you were to further isolate, say, everybody over 30, the results would probably be even worse.
American society does, in fact, have deep-rooted problems with homosexuality. That's why we used to have so many anti-sodomy laws on the books, and why it took until the 2000s for the US Supreme Court to actually shoot them down. It's also why the Defense of Marriage Act was passed. It's also why
almost the entire anglophone world except us (see:
http://en.wikipedia.org/wiki/File:World_homosexuality_laws.svg) has legalized/recognized the validity of same-sex marriages or unions. Things are getting better, yes, and there are worse places, but we're still one of the worst when it comes to the English-speaking (or, really, Western) world, and to say we don't have some pretty bad problems is naive.
There's also the fact that the US, being the US, has a lot of variety between states. Try asking that question in, say, Alabama or Kansas.
Also, here's something from 2009:
http://www.gallup.com/poll/118378/majority-americans-continue-oppose-gay-marriage.aspxNote how godawfully split the opinion is between liberals and conservatives. That is not good. Even 23% of "liberals" in 2009 didn't support even the
recognition of same-sex marriages, and a whopping 80% of conservatives (a pretty big supermajority) felt the same.
Oh, and only
13% of those responding thought that allowing same-sex marriage would change society for the better, compared to 48% who thought it would change for the worse.
It's easy to say that a small majority is "enough for change", but keep in mind that power players in politics, lobbying, etc., still exist. There's a reason Prop 8 in California was passed, and why it's so damned hard even in fairly liberal states to get pro-gay-marriage legislation through. The situation is improving, but it isn't easy.