its not only minimising risk though is it?
Can you tell me statistically, which is more likely?
a) leaving 3 children in car while paying for petrol, nipping into corner shop etc
b) taking all 3 children out of the car, across forecourt, into large shop yokey. Bearing in mind you need one hand to hold the baby, one hand to get your cash/card out..whose holding the toddler, or the slightly older one.
You can't really tell me can you? It is my job as their parent to decide that for them, I do not need you to tell me.
And as for being"disgusted at being ridiculed for not risking it", those you say are being ridiculed are the ones calling those of us who do it, lazy, irresponsible, negelctful, abusive, and practically murderers. You don't think we are allowed a little barb in too? 
Life isn't about minimising all risks it is about balancing them. If it was, crossing a road with a child is off limits unless strictly necessary, as are a million other things. Living is risk. You choose for yours, I'll choose for mine, how about that?