I know, I know... but stealthy it wasn't.
I dunno... there's a few different kinds of stealthy:
1) "No Trace" - You glide through the building like a midnight breeze, a ghost of flesh and metal, leaving not a single sign that you were ever there. You carefully avoid, or spoof, the security systems and sneak past guards.
2) "No Alarms" - You don't give a crap if people know you were there, as long as you've got your objective and are out the door before the shouting starts. You hack or EMP security systems and 1-hit-KO the guards you can't avoid.
3) "No Witnesses" - You don't care if they see you coming, as long as they don't have time to scream for help, because you don't plan on leaving them around to tell anyone. Moar Dakka: Silenced Battle Rifles, chemical grenades, and breaching charges are the norm. The heavy troll gets to dual-wield MGL-18s
Seriously, which of us wouldn't have killed the mass-murderer-in-the-quadruple-digits Joker by now, or even any of his OTHER Arkham Asylum cronies?
I'd probably spare a few of them but, yeah, for Joker, Scarecrow, Crock, and a few others... bullet to the brain-pan, squish.