I want to rewatch that scene because there was something Cas was trying to say without saying it to Dean. I figure because of how quickly the angels snatched Anna, someone's watching him. And yes, he crossed a line with the Archangel thing. But he did what he thought was right at that point.

Someone up there minded a lot. Enough to have him kidnapped and then get him to tow the line somehow. It's crazy up there.