I agree intent matters. My point is that harm here is the catalytic converter being stolen, not the unfortunate chain of events that might befall someone as an indirect result (and other things that can cause that indirect result aren't even crimes). That unfortunate chain of events can't be used to justify murdering the thief of a relatively inexpensive car part. It's like saying a pickpocket should get murdered because they might steal your bus pass and that's how you get places.

For the record, I'm immune to catalytic converter theft because I don't own a car. I've had bike wheels stolen multiple times though, and that's no fun, but certainly no justification for murder.