That is very true. Those who take pleasure in killing are always somewhat... unsettling, even if it is for a justifiable cause.

[Looking at you, General Grievous. Please never get Ported in, Dooku doesn't want to have to explain why he hangs out with you.]

But there are other passions one could feel while taking a life. Fear, or anger come to mind. Some might consider them to be ugly emotions... but they are natural, and powerful, and useful in aiding our survival.