Haven't had time to read all this thread, but earlier this week I went to the supermarket...
The car in front was waiting for the last Parent & Child space, and I was about to drive past when I noticed that there was no kid or child seat in the car. So, feeling righteous about it, I waited until the guy had parked, then as he got out, started with "Excuse me, you do know that's for cars with children..."
I was stopped in my tracks as he got out, turned round, and clearly had only one arm. So the rest of the sentence sort of died in my throat.
Of course he totally blanked me, and I wanted the earth to swallow me up.
I have no problem with a driver with a mobility problem using the parent & child spaces if the disabled spaces are all taken, but having seen friends with toddlers & new babies struggling to get toddler into trolley, baby in sling etc., anyone without a genuine reason for using them should be a bit less selfish.