i'm not arguing with the premise. but it's like arguing for abstinence instead of contraception. it's ideal, but not realistic. you need to give pet owners responsible options to mitigate the effects of the heat in the situation that you have to leave your dog in the car for a few minutes.
i'd argue lengthy periods are problematic because it's confinement. if you're going to be gone a long time, drop your dog off at home first. or don't bring it in the first place. but that's not the same thing as stopping for groceries.
i'm assuming that the fan will mitigate the problem to a reasonable level. i don't have a car (or a dog) so i can't test this. but these videos should integrate two base conditions to provide for a more realistic simulation:
1) the a/c should be on for a while before you get in the car. because, if you're leaving your dog in the car, then you're driving somewhere. and, you have the a/c on.
2) leave the fan on.
i would have to think that that should at least extend the period of time you can safely leave your dog in there - if not indefinitely (and that's neglectful, anyways) then at least to a point where you can get in and out without worrying that you're killing your pet.