It wasn't perfect, Cas. Humans being vessels for angels is never going to be perfect, I don't think we're really meant for it. I mean... it's intended for us, that's the way things work with angels on earth, but sometimes I think that rule is more about stopping you from being all-powerful than about humans really being meant to be used as your weapons.
But you didn't try to leverage his daughter's life against his. You were trying to give him an out, while still protecting his family and everyone else. Intentions matter. They're very important.