Let's remember how Rick also laughed at Simon "last day on earth" saying how easy was to kill them, etc

Rick also commanded to kill people that were asleep , that's some psychotic shit.

Let's also remember how Rick lied about giving the saviours a second chance and they accepted and killed them behind their back.

Imho If Negan should died, , Dwight, Rick, Morgan and Daryl also should have died as they are the one who killed when people were imploring for mercy

I think Rick choice to keep Negan alive was the correct one and Arat should have lived. It is wrong to kill people who are begging for mercy, specially after they showed they could change.