When did Clark ever kill on Smallville?
I forgot which episodes...but here they are.
Clark attempted to kill Brainiac (only to find out later, he had failed). Still, the intention was there.
Clark also killed Titan (I think that was his name). Now, some may see Titan being punch up high then landing on his own stake as a, "Clark didn't really kill him" kind of thing, but Clark DID kill him. Clark's fight with Titan resulted in Titan's death and Clark went into that fight with the sole purpose to kill Titan.
Clark also killed Bizarro Clark after Bizarro Clark masqueraded as Clark for a time by using Bizarro's weakness to (I think) Blue Kryptonite.
Clark also "accidentally" killed a Super powered assassin who had been experimented on my Lex Luthor. I forgot his name, but Clark blasted him with Heat Vision and he died. If I remember correctly, it was one of Lois's former boyfriends who was a soldier then his death was faked so Luthor could experiment on him.
Then he preaches to the Legion of Super-Heroes, "We don't kill! There is always a better way!" I agree with this statement, but where was this mentality with Titan? Brainiac? Bizarro? Clark proved himself a hypocrite. He did one thing then said another.
He chose to NOT kill off Doomsday, and all those other ones that you mentioned were not due to him directly killing them off, but that they happened to in a sense get themselves killed off!