His ego is too big, and getting bigger. He wants fame and glory for the hard work he's done. I think the fact that Walter is asking for the names of the 9 guys in jail/prison to silence them is proof enough he'll kill if threatened. I think under the right circumstances he'd kill Hank, Skylar, Jesse, or Marie without much thought. Walter White from season 1 or 2 maybe, Heizenberg today, no way.