Here's a reason to be a skeptic that holds up at first, but crumbles on reflection: religious beliefs depend on where a person lives. Via Jerry Coyne, here are two amusing maps:
If having a belief depends on where you live, the suspicion is that the belief is shaped by non-rational forces instead of being a consequence of the way the world is. We shouldn't take these kinds of beliefs too seriously, if at all.
And yet, and yet. The likelihood of believing in human rights, or equality for women, or same-sex marriage, or democracy ... all these beliefs would go on Map #1. They vary from place to place. Nevertheless, you could make a case that liberal democratic views on these matters are rooted in the way the world is. I'm not going to become a skeptic about women's equality, just because the folks in Afghanistan and Saudi Arabia don't believe in women's equality. So why should anyone take sheer geographical variation as evidence that the tenets of some religion are false? Bad precedent!