Board Thread:General Discussion/@comment-36143601-20180921001309/@comment-31593032-20180921021457

1. As a soldier, Undyne was likely taught that humans are evil creatures and incapable of compassion.

2. In a lot of battles, fighting them to the point of near death can be self defense. But killing them is not. They would have gladly fled the battle at that point and you could have spared them.

3. For a little kid, you seem to be capable of a lot of murder... how would you feel if someone killed your friends, regardless of if it was a kid or not?

Undyne attacking you on the pacifist route is definitely wrong, but on the neutral route she has a reason to. Even if killing isn't the best method.