Lord Vader wrote:
We all know that Dean's messed up. Even he admits it. But he also sees the world in a much more black-and-white light than Sam does. He sees a monster, he kills it before it can kill him or another human. I thought it was very in-character for him.
Also, as a Doctor Who fan, I loved the Amy Pond reference.
Well Dean can and has made distinction about monsters before. You kill a human you die. So yeah I agree very in character.
Lenore didn't kill to his knowledge (she lives), non spirits who don't harm, he doesn't remove. You kill (pretty much for whatever reasons) your going to die.
Hell even Ruby, he wants her dead, so dead. But Ruby goes to great lengths to never harm a human, and with her "helping" Sam he lets her live. He finds out she is playing his brother she is very, very much toast.
It's very consistent for the character.