It kills the fun in killing them.

We respawn under the same name, don't we?
Permanently killing NPCs should be possible only for very important NPCs, like a faction leader. The faction would get a new leader but it would be in some disarray and that faction would become very hostile towards you and your guild, if you are in one.

Marshals in my mind qualify as rather high ranking faction leaders.

As Beolach says, they are the highest official NPCs in this game. The few I killed belong to a faction that is very hostile towards me and my guild; I don't expect to see that faction being nicer after those kills; I was just hoping that my act of vendetta could leave traces there.

Correct me if I'm wrong but other defbots do not respawn under the same names. This morning, I was also planning to suppress a Serco defbot with an Itani name (Bess), ie a traitor, but could not find it where it was before.

EDIT: I verified it, the defbots respawn under a different name