In all likelihood, the carjacker is already armed. No one tries to mug someone without an advantage. But assuming they are not, it forces the carjacker, who is

In all likelihood, the carjacker is already armed. No one tries to mug someone without an advantage. But assuming they are not, it forces the carjacker, who is a human being, to wonder if his/her line of work is worth having some crazy asshole open fire over some stupid car. Most people would say no, and the ones who decide it is worth it, they won't last long if half of the jobs they pull end up with bullets coming their way.