Not absolving the carjacker in the least. He committed a crime and is totally responsible for it. Just because the opportunity is there and made easy, he's no less culpable.
I just get pissed at people who are that careless with their little ones. Even if the car hadn't been carjacked, the 5-year-old could have climbed behind the wheel to play and set off a tragic outcome. Or what if it wasn't a carjacker but a kidnapper? It's just always stupid and negligent to leave kids unattended in a running car on a city street.
I get your argument and I agree with your point, just as when rape victims get blamed because of how they were dressed or where they went at what time, etc. A criminal is always responsible for his actions. That wasn't intended to be my premise but I see how it could be read that way so I maybe I could have written it better.