Often, new mob inductees need to commit a murder before getting straightened out.

Innocent men also get whacked by the mob. It could be a union official that won't cooperate with demands from the mob. Or a sanitation operator that won't play along with bid rigging. Or somebody might be in a position to potentially hurt a mobster in an upcoming trial. Sometimes, a mobster could be in competition over a woman. Many times, a murder entails someone getting double crossed.

I believe the bottom line for both gangs and the mob is they need to kill who they are ordered to kill. Their personal opinion on whether or not the victim deserves to die is not taken into consideration.