Reed Richards wrote:
Given the code against killing that heroes operate under, I still have to ask (I may be too deep in a deconstruction frame of mind) how could you as a person of any conscience NOT kill Bruce Banner, or say Magneto or Venom? If you are a hero with the capability to do so, and you let this guy continue to operate, how many of the murders he might commit fall at your feet?
This was addressed in The Dark Knight, I think - when Joker was trying to turn Batman. By killing the villain, you're proving you're just as corrupt as the villain is. Yes, you might be doing what is necessary, but it is still a crime. Their murders do not fall at your feet, they make their own choices and you are not responsible for their choices. You can only do what you can do and stick to your gut and your heart and your way of thinking.