it's not about the act of killing for revenge or anything.

I don't think you are wrong in my own context, but in areas with essentially no hope of recovering from a life-altering theft, I can see it. In medieval times, right up to the modern era, where state police that (ostensibly) serve everyone were actually instituted, policing was essentially a private service. It was on the individual and whatever posse they could muster to get their stuff back.

For me it's one of those situations where I don't agree, but I understand. Not for basic goods obviously, but I won't shed many tears if someone gets killed while trying to steal someones phone/car/bike/etc. Like, look at Brasil. Are you saying it's pathetic for someone to shoot a thief who just jumped off a motorcycle and tried to snatch their purse?

I just feel the more pathetic of the parties is the one trying to steal.

It's about making future threats credible.