As the regular readers know, I'm a member of the campus group called BASS, which stands for Bruin Alliance of Skeptics and Secularists. Note that the A does not stand for atheism. It isn't an atheist club, but it is. We advocate skepticism and secularism, which are not atheist-exclusive (I would hope not), but we're also the only group on campus to represent atheists.
Does that mean our group has two roles, or one? I don't think anyone would go so far as to say we should exclude theists, but there are a number of people who think of skepticism and atheism as the same thing, or closely related things. This is debatable. However, I think they are two different ideas, and I think you should think so too.
I will begin by conceding that skepticism and atheism are related. At the very least, they are correlated. But I think it's more than that. Skepticism actually causes people to become atheists, and atheism causes people to become skeptics. Anecdotally, I became an atheist because I carefully considered arguments while under a skeptical mindset (meaning, an open-minded, but critical mindset). And many atheists are highly sympathetic to the goals of skepticism, because they realize that religion isn't the only source of strange beliefs out there.
Furthermore, I think there are good reasons underlying the causational link. Not that skepticism logically entails atheism, or anything so direct. But I do think atheism is more in the spirit of skepticism than theism is. I think the idea of appealing to an unknowable entity in order to explain the universe, or for pretty much any purpose at all, is not good skeptical practice. Even for deism or fideism, my thoughts are along the lines of, "I don't find that very compelling, and I don't think you should find it compelling either."
But of course I would think these things. Of course I think atheism is more correct than its alternatives. I wouldn't be an atheist if I didn't.
The thing is, there are a ton of things that cause disagreement among skeptics. When I first subscribed to Skeptic magazine, I found that I disagreed with a third to a half of it. That is totally how it should be. Obviously, if there's an article about investigating a paranormal claim, I would expect it to be a well-designed investigation with a more or less definitive conclusion. But a lot of these are opinion articles, or they are detailed interpretations of complicated bodies of evidence. If you're not picking out lots of specific details that you disagree with, you're not doing it right.
Religion is very clearly within the region of "stuff that skeptics disagree about all the time". And it's a very popular topic too, because everyone seems to have a unique opinion about it. I've spent years in the atheist and skeptical blogospheres, and I still occasionally see a perspective that is unusual and surprising, and not in a bad way either. I find that the variance of religious perspectives is much greater than the mere difference between atheism and theism. If we were to exclude theists from the skeptical movement, to be consistent, we'd have to exclude a lot of atheists too. We couldn't possibly be so conformist.
To finish this off, I'd like to make two imperfect comparisons to give two different angles on how religion relates to skepticism.
First, religion is like politics. It is not a standard skeptical topic, but skeptics certainly tend to be politically conscious, and tend to enjoy discussing it. Libertarianism is not considered to be the same as skepticism, partly because less than half of skeptics are libertarians, but also because it's a completely different idea. Even if every skeptic were a libertarian, and if skepticism really did lead directly to libertarianism, we would still not consider the same thing. It's a difference of area of application, and a difference of method and conclusion. If you agree with the skeptical method, but by a strange twist of reasoning, come to an uncommon conclusion on one particular non-standard topic, you're still a skeptic.
Second, theists are like women or ethnic minorities. Lamentably, there aren't many of them in the skeptical movement. For whatever reasons, skeptics tend to be predominantly white males. There should be more minorities and women! Not because we want to be able to say, "We're so diverse and tolerant," but because we should be equal opportunity. I don't like the idea that half of the population is for whatever reason less likely to be skeptical than the other half. Similarly, I don't like the idea that religious people are less likely to be skeptical than the nonreligious. I don't care if there's a good reason for it. It's still sad.