It doesn't make a damned bit of sense, and one day soon he and Gabriel are going to Have Words about what he'd done. But not today. Whatever's going on, Sam wants to handle it and Dean has to let him.

"All right Sam. I'm gonna grab a bite to eat, hit the road in a couple of hours. You change you mind or anything, you call." If Gabe was really mortal now, he could trust Sam to handle things.