An interesting point, Ted, but no, not entirely. Of course these are messy and arbitrary categories; maybe even somewhat circular categories, in the sense that if I find someone I read or argue with infuriatingly self-righteous I'm likely to put them in the right-hand column and not the left.
But I know several New Atheists; some people who I treasure greatly and find generally sensible and compassionate do seem to believe that it would be sensible public policy to ban the teaching of religious beliefs. And most of what I mean by traditional christianity is based on reading; most Christians in pre-Enlightenment Europe seem to fall in the left column.
Some new atheists, like Sam Harris in this debate seem to be well-meaning, courteous, and in good faith. So do some fundamentalists, I imagine. Even then, though, their fundamental attitude to the world seems characterized not by awe and wonder at the mysteries of the universe, but rather by a mix of irritation that other people can't grasp the obvious, and suspicion that really the other people are simply refusing to get with the program due to moral cowardice.
What I'm calling "new" atheism isn't really a new phenomenon, but it seems to have experienced a massive surge in popularity after 9/11. I haven't read enough Mencken to slot him; Twain (like his latterday lookalike and kindred spirit, Vonnegut), feels like an old atheist to me. It's hard to imagine Twain taking science seriously as an answer to all human problems, one that renders religion obviously irrelevant. Twain mocks everyone, and, while he may not think religion a terribly good idea, he is most interested in attacking the vices and abuses of its practitioners, in the classic Chaucerian style, rather than arguing that its truth claims constitute a pernicious mental virus.