After giving this some more thought, I'm coming to a conclusion that while the intent is just (stopping criminals), as Jaeger pointed out, the average person is ill-equipped to stop a crime and even less prepared if that criminal reacts dangerously. Who knows if he/she has a weapon? Is it worth a life, your own life? I think that's what the officer in the article was talking about when mentioning the severity of the crime. At the end of the day a keyed car sucks, but again it's not worth a life.
I like to think I would interrupt a petty crime, like shoplifting, but again who knows who has a gun or a knife these days? TTC booth operators getting shot at close range for a few dollars? It's sickening.