Well, yeah, "murder" is generally wrong. But still case-by-case basis; sometimes it's the only and/or best form of justice. I, personally, have never murdered anyone, but neither have I been in a position where it looked like a good option.

Look, if potentially killing people is part of your job, then you'd best be mentally prepared, and killing better not be a big deal in general, except from the standpoint of potential legal repercussions, if your actions aren't entirely justifiable. Why do people think they have military recruits singing cadens about clubbing baby seals and dropping napalm on Vietnamese villages? (They're not supposed to teach those songs anymore, but they live on). The idea's to desensitize.