It seems to me that Adam Frank doesn't do himself any favors in this debate by linking "spiritual endeavor" to religion. While one can argue that "spiritual endeavor" is the basis on which most religions are founded, if one wishes to debate the subject with an atheist it is probably better to not bring up religion at all.

You're more likely to have a fruitful conversation if you discuss "understanding the true nature of subjective reality" rather than "spiritual endeavor", "the overview effect" rather than "religious experiences", and neurological research rather than the Bible.

But even then it is probably pointless. The Buddha says that a student only obtains proof of the validity of his teachings when he becomes a Sotāpanna. Before that, the Buddha's teachings must be taken on blind faith -- not something any self-respecting skeptic is going to do.