Harris/Sullivan Follow-up

I've been rather busy lately, so I'm late to post this. In case you haven't noticed, Harris has responded to Sullivan's last email. I think Harris gets to the heart of the matter with this paragraph:

You want to have things both ways: your faith is reasonable but not in the least bound by reason; it is a matter of utter certainty, yet leavened by humility and doubt; you are still searching for the truth, but your belief in God is immune to any conceivable challenge from the world of evidence. I trust you will ascribe these antinomies to the paradox of faith; but, to my eye, they remain mere contradictions, dressed up in velvet.

It is this kind of cognitive dissonance that worries me most regarding religious progressives. Partitioning their brains in order to preform such mental gymnastics must have some kind of negative cognitive effect in the long run. Why don't they just take the next logical step in their reasoning?