As opposed to frivolously ...

... On seriously doubting the existence of God. (Hat tip, Dave Lull.)

I remember, when I was studying scholastic metaphysics in college, that the professor told us we could shake up everybody at the dinner table on Thanksgiving by announcing that we had learned that God does not exist - the point being that the word exist strictly means "to come out of something" (i.e., to derive being from something else) whereas God just is. "All things," Aquinas said, "run to mystery."
There is, by the way, more intellectual heft in this single blog post than in all that the Dawkins-Harris- Hitchens troika have written on the subject.