Just because it's the job of the military to kill people doesn't mean it's okay.
That depends, I'd say. Killing an enemy who is attacking or invading your country, or poses a clear and present danger to your country's security is OK, IMO.
Interesting that none of the comments so far talk about the blatant privacy violations that facebook commits on a regular basis. Even more so, nobody talks about the fact that violating your privacy - or convincing you to willingly give up private information - is the very business model of facebook.
All of which you agreed to when choosing to use Facebook. Believe it or not, you don't have to use it.
"Engineering without management is art." -- Jeff Johnson