The dance of the angels of DEATH

An angel of death is a type of criminal offender (often a type of serial killer) who is usually employed as a caregiver and intentionally harms or kills people under their care.

How many of them did realize at some point that they were harming people, but carried on injecting regardeless? "I had to play russian roulette its your turn now!" mentality perhaps?
Denial? Sunk cost fallacy?
Something about those nurse and doctor dances always rubbed me the wrong way. Guess most of them are just NPCs.