Why do people hate afk kills?

I’ve noticed that a lot of expert lobbies have rules and that even if there are only a couple rules “no afk killing” is one of them. Some say “no afk killing until r3,” but still. If they are afk then they aren’t playing anyway, what’s the harm in killing them. If they are gonna come back in a few rounds I still don’t really understand the harm. They might die when they are moving, so why should I spare them if they are standing still and in a place easy to kill. They can do their tasks easier as a ghost anyway. To be clear, I don’t break lobby rules that hosts set, I’m just questioning why this is a rule in the first place.