Ever see the movie "No Country for Old Men"?
My not so nice 'courier' was similar to the guy with the coin toss fetish.
I didn't snuff everybody... but a random person in every settlement or camp ended up with a terminal case of... something.
I tried to get creative, which made it fun even for a goody two shoes (me in real life).
Mines, C4, sniper shots, reverse pickpocket with a grenade, lure a radscorpion into a group of NPCs... I even went on a Brahmin tipping rampage.
Mwah hahahahaha
I still felt guilt, but kept telling myself not to be silly. It's role play and the only thing dying is pixels.
It helped that I wasn't slaughtering everyone and everything. I just left enough bodies laying around to (supposedly) confuse/scare the locals.
About the time I got to the Strip I got tired of it and re-started from an early save.