"Killing is wrong, no matter what," is a very powerful and standard meme for heroes.

It is counter intuitive for someone who "loves people" to kill someone. It requires a less-biased assessment of expected utility than is typically performed. That's why I enjoyed the original quote; in the context of the movie, it made sense in the way of typical human failings for him to say no, and his body language and tone highly suggested he would do so right until the end.