I dont know if its right or wrong to legislate what should be logical. But one thing I've found in life is that there is nothing "common" about "common sense". Matter of fact, the average person does some pretty stupid things during the course of a day. Especially if they know no one is going to do anything to them for it.
What is the most common major crime committed here? Auto theft. You gonna not only leave your keys in the car, but leave it RUNNING? And then expect a car theif NOT to take your car? In my mind, parents who leave their kids in a running car just to do a "quick" errand ARE endangering their kids, because they KNOW there's a damn good chance that car will get stolen! If they stop to use their brains for one second they would know that. Leaving the kids in the car is just lazy. If they do this they deserve what they get. I'm sorry, in most cases I am all for promoting the responsibility of the individual, not enforcing it through laws. But we are talking about little kids here, that are unable to look out for themselves. The parents are supposed to do that, and keep them safe. If they are failing because of sheer laziness then we need to provide an incentive to make them do the right thing.
When my son was young enough to be in a car seat, even going to the gas station and filling the car up, when I was done I unbuckled him, carried him inside, paid and put him back in the seat to leave. Even for a 30 second "errand" I NEVER left him in the car. I may not ever win any award for being a good father, but I love my son more than anything. No way was I taking a chance. If these parents care about their kids, then they need to be put on notice that bad things happen if you leave them in the car. Ignore that warning, bad things might happen to you.