WHile its true that Dean is always amore inclined to be the one to jump to lethal force, he more then Sam sees his calling in not only hunting but saving innocents.
Previously all the times Dean has used lethal force is when they realistically haven't had another option. The only exception was Gordon (going back to season two when he is trying to kill Sam). Dean absolutely was going to kill him. But of course that was also because he was trying to kill the single most important thing in Dean's life. Give Dean any other way (and it not being someone who is gunning for Sam) and he would take it.
Gotta disagree with you here. Heck, that is one of the RATHER LARGE bones of contention that Sam brings up about using his powers. The host actually has a very good chance at survival. In Dean's world the host is expendable to save OTHER innocents. He doesn't place value on the hosts lives like Sam does. They are mere collateral damage of the war and such is life to him.
While Dean did say that in his confrontation with Sam, it doesn't fit with what his actions have been. In fact it plays more to his fear about what Sam could become, then anything else.
Lets look at them. Dean has killed several or tried to kill demons going back to the 1st season.
1. YED kid attacking Sam in Devil's Trap
2. YED All Hell Breaks Loose II(there is a full season where they don't kill any demons because they don't have the means).
3. Ruby in Malleus Maleficarum
4. Ruby's former boss Malleus Maleficarum
5. One or more Demons in No Rest for the Wicked
6. YED In the Beginning (in the past).
7. Ruby in Metamorphosis
8. Allistar in I know what you did last summer.
I think that is all. In all of them he had either no other means of harming them or he let Sam try and use his psychic abilities to stop the demon.
On Ruby he has tried to kill twice, but I think in both times it was more for her influence on Sam then any "evil" she had done.
Certainly when she was trapped in a Devil's trap he let her live.
But he has encouraged non lethal force on a several occasions. One trapped in a devi's trap, doesn't use lethal force, female in Sin City tells Sam to not shoot her (he does). Has let several demons walk free instead of stopping them (either because he choose not to like in Crossroad Demon) and several in the dinner in Lazarus Rising (when they did have the knife. In Jus in Bello Dean is unwilling to let a women volunteer her life to save to kill the demons (including Ruby).ability to stop demons he tried to kill them pretty much every time (the exception is Ruby and one Demon caught in a devil's Trap).
Absolutely Dean will kill when he sees that has his last option (and he will come to that conclusion typically faster then Sam). But when given an option, Dean typically will not go for the kill (with the exception of something he sees as a real threat down the road to Sam.
If it wasn't for Castiel's warning (and meeting YED and hearing that his plans didn't end with raising a demon army), tehn I don't think Dean would have the same problem he currently has. SUre he wouldn't like it (he doesn't typically like anything supernatural). But he would be for Sam using it.
And Sam knows this about him, and I am sure he sees it as a double standard.
And lets face it, clearly in the Halloween episode as much as in tore Dean apart to see Sam using his abilitites, Dean understood that he had to.
