Smallville raised a fairly interesting moral question last night: is it ever OK to kill someone? Oliver Queen wanted to kill Lex, but Clark was determined to stop him because killing is wrong, no matter how evil the person is. Eventually Lex was killed (we all know he's still alive), leading Oliver and Chloe to have a conversation about whether it's morally justified to murder a monster like Lex Luthor.
It's a morally gray area, and one every comic book hero has to face. Murder is wrong, but evil men like Lex Luthor are never going to change and are irredeemable. A hero's duty is to protect the citizens, but does that include killing one to save the rest?
On this issue for Smallville, I would tend to agree with Oliver Queen. Lex has proven time and time again that his primary goal is to control the world, possibly by using Clark's abilities or simply by getting rid of him. There is no hope for him, and as Clark was told, Lex isn't the same high school kid Clark met back in season 1.
What leads me to this conclusion is that Clark seemed to agree with Oliver. After Lana disabled the Krypto-bomb, Clark went after Lex and it looked like he finally came around to the same conclusion Oliver did. Lana stopped him, and Oliver beat him to the punch, but aside from those factors, it looked as if Clark was finally ready to end it himself.
This moral ambiguity adds a lot to the show, and it seems to be the newest trend for The CW's Thursday nights. While both Smallville and Supernatural are typically about the good guys defeating the bad guys, this season both Clark Kent and Sam Winchester are facing tough decisions.
Clark has had to choose between killing the Brainiac-possessed Chloe and now whether to kill Lex. Meanwhile, Sam is debating whether to kill a little girl named Lilith who is possessed by an evil demon.
Now that Lex is allegedly dead, Clark may think his decision is over, but we know that Lex will keep coming back, so Clark's days of living in the gray area are far from over.