I'd be interested in hearing non-US perspectives on this. Is it acceptable elsewhere to leave your small child alone in the car for 5 minutes while you get something from a store? Would you fear for the child's safety, of legal action, or neither? Is the US leading the way criminalizing parents who do such things, or are there other countries that have been doing this for years?
I don't see any issue with people leaving their kids in the car, it just requires a little common sense.
Also, comparing events where someone forgot their kid was in the car and leaving them all day to events where the parents consciously leave their kids and are aware of the conditions they've left them in (especially if they actually do something to help ensure the comfort of the child, like cracking the window) it's completely wrong. One is neglect, one is giving your kids a little freedom.