The last archangel we faced, we locked him away cause killing him wasn't an option. These guys are way powerful. You've seen Cas and Anna? Nothing compared to what these guys can do. There are ways but we're not gonna get it done easy.
But Purgatory, this is the place that the biggest baddest demon I've ever known wouldn't touch because he didn't know what would happen.
Crowley's not offering this out of a power play, this could mess him the hell up just as much