Depends on who they are, really. Civilians, cops, Trauma Team? Won't kill them. They're innocent and/or just doing their job, don't got no beef with them, can just run if I'm in serious trouble.
When it comes to gangs, though, I won't care so much about using lethal force. Especially on gangs like Maelstrom, Tyger Claws, Scavs, etc. I'll probably sneak my way around or charm the Moxes and 6th Street, but I wouldn't be TOO hesitant about using lethal force there too. Valentinos I haven't seen enough of to really determine, same for the nomad gangs.
When it comes to the corps, it's a toss up. I won't kill the corp cops and security guards for coming after me when I trespass, but if I see corporate employees doing some messed up shit, like shooting down innocent civilians etc, then I just might be judge, jury and executioner.