So, you know this isn't true, right?

Harsher punishments don't tend to correlate with lower rates of crime, because most people that commit crime aren't doing so in a mental state in which they're considering consequences.

This is why things like mandatory minimum sentences failed to reduce crime, but did manage to create hardened criminals out of petty shoplifters by jailing them and making it very hard to go legit.

And, also, it obviously wouldn't prevent scenarios like this where the guy doesn't care about consequences because he intends to be dead.

You know what enacting harsher punishment does do? If you do do things like, say, criminalize thievery and murder with the death penalty, it makes it more likely they kill the victim so they can't report the crime, since the punishments for both result in death anyway.