Off-topic: ExcellentThe trick was sneaking around and taking every enemy out with a silenced headshot from my revolver. Those were certain one-hit-kills, so as long as I was on-target, the enemy I engage doesn't get a chance to detect me. If there's a cluster of enemies together, I kicked in Sandevistan before I started shooting, so that I had time to headshot/kill the whole pack of bad guys before the first one's brains had finished decorating the floor. They didn't get the chance to detect me.
Sure, they were in "alert" status, because a few dead bodies were found but they never went all the way to "detected" status. In fact I used dead bodies to draw-in more victims a couple of times. "Oh my god, what's happened to Fred? There must be a sniper nearb-"
Stealth is sometimes required because many build can do it.
They can't really require "You must kill everyone violently"