After eight seasons, the thing Supernatural does best is build on the consistent characterization of the two brothers. It is what keeps me watching.
Dean did a very bad thing. He allowed Sam to be possessed, actually tricked him into accepting Ezekiel, when he knew Sam would never do it if he knew the whole story. That’s bad. It’s really, really awful considering Sam’s past experience with angel possession. But is it out of character for Dean to do this? I don’t think so.