Stayingsantagirl - you asked for a civil response, so here goes.
As I mentioned earlier in the thread, I would bet good mony that most 'upsets' or tantrums as people call them are indeed caused by hunger, low blood sugar in most part.
It's not generally in response to a 'tantrum' (hate that word) that I will feed ds2 something on the way round - it's to pre-empt one. For instance yesterday in Sainsburys, we got him INto the trolley, but once we had been in there about 20 minutes and got nearly everything, we ended up at the cakes bit, and they both asked for a cake - so I got them one each, they barcoded the little bags and we made our way through the crowds to the checkouts...ds1 asked for his cake when we had been given them, and I said no, I think you can wait a while (he is 6) but ds2 was handed his immediately, and started to eat it happily. Of course I kept the packet safe, and when he had had a few bites he had had enough and we put it back in and resealed it.
He did still get fed up just as we went through the checkout - he wanted to get out and run about, and actually climbed to his feet despite my having the straps on their tightest setting - great - nearly a fractured skull like the other MNer's child who fell out of a trolley - but I managed to shove him back in sideways and he waited the next 5 minutes in relative peace without yelling at all. Tantrum avoided.
This is why I do it. If i hadn't fed him something to keep him going, he would doubtless have made it hell for everyone at the checkout, but he didn't feel bad enough because he'd been fed.
I probably ought to take something as a precaution but it is almost certain that he will refuse anything 'boring' brought from home, so it would defeat the object (he is simply in that phase and not a good eater)
So I do equate it rather to breastfeeding on demand. I'm still waiting for anyone here to admit that they object to babies being breastfed, or indeed bottle fed, in public, at awkward moments in order to avert a full scale meltdown.
I admit it feels slightly wrong to feed my child from an unpaid for packet, and I rarely did so with ds1, but I see it as sometimes the lesser of two evils.
HTH.