Irrationality will wipe itself out, regardless.
I'd like to think that's true, but I don't. To me, it's more like women's suffrage. Women getting the vote wasn't something that was going to happen inevitably, given enough time. People had to force the issue. Same with irrationality.
Why do you think the dark ages didn't last forever?
Because freethinkers challenged the status quo. You don't really think the Church gave up all that power willingly, do you?
Leave the USA to the fundies and they'll create their own hell and die off.
If the USA were some Third-World backwater, I might agree with you. However, the USA is arguably the most powerful nation in the world, and certainly one of the most imperialistic as well. It cannot be left to its own devices; it must be shown the error of its thinking because, if it isn't, it is highly likely that it will harm not just itself but others as well.
I believe it was Thomas Jefferson who said, "My country, right or wrong. When right, to be kept right; when wrong, to be put right."