Why belief in the Devil should be considered especially odd escapes me anyway. If Jesus Christ was the personification of good, why shouldn't there be a personification of evil?
In case the sidebar isn't clear enough, I believe in neither. But what I find curious are atheists who pick and choose what parts of Christianity are stranger than others. It all starts with a talking snake, for heavens' sake. If you don't accept what's in the Catholic catechism, but instead in some sort of amorphous universal love thingy, you're not actually a Catholic, and I see no reason why you should be acknowledged as one. Conversely, if you pick and choose some parts of the doctrine to be sneered at as especially odd, be prepared to be branded intolerant of Catholicism. Me, I think all religion is odd, but it would be foolish to consider embrace of religion as a irremediable personal flaw.