he wasn't tamed. he knew what he was getting into, and he wanted to do it, despite his pleas to the audience. he was a bad, merciless man, and we only liked him because the movie taught us to side with vengeful prostitutes and greedy hired guns. it was a great performance from clint.
if he convinced you he was tamed, pd, then he did a great job, because that's what the role was supposed to do: make you forgive a psychopath until his nature is fully revealed. if we hadn't believed him, the ending would have been meaningless.