simplest argument is often the best

Slacktivist; Your Not Allowed to Kill Civilians

It's been awhile so it seems again it's time for a helpful reminder that noncombatant immunity isn't just a good idea, it's the law.
In other words: You're not allowed to kill civilians.
Killing civilians is against the law. Killing civilians makes you a criminal.
Yes, but ...
No buts about it. You're not allowed to kill civilians.
And, also: You're not allowed to kill civilians.

So simple and straight forward, how can you argue with it?

Thank you Slacktivist.