Was he leaving it on for periods of time that were long enough to cause suffocation?
I highly doubt it would have hurt him with his mother and other people right there watching, unless perhaps he was leaving it on his head for a minute or more at a time.
I would have said nothing. If the child had put it on and left it there for an alarming amount of time then I would have said "Oh sweetie, I think that's long enough!"
As for the bag ripping, unless he was biting it or clawing it, I really don't think that the produce bag would have just ripped sending a small piece flying into his mouth. And if it had been a grocery bag with tabs, I'd have just casually said to the mom "Hey, I am NOT gonna berate you for letting him play with the plastic bag" *friendly grin* "But I just wanted to mention that you might wanna check it for those lil plastic tabs first, because they come off easily and are a real pain in the butt if they get in baby's mouth!"
I agree that sometimes don't judge me does mean don't make me feel guilty for my bad choices. But there are some choices that are bad to some, good to others. I wouldn't feel guilty if someone judged me for letting my son play with a produce bag, even if he put it on his head and took it off. I would just feel like they were being hypervigilant. Sometimes don't judge me means hey, maybe I do care and just see it differently than you. So far my son has little interest in plastic bags, but if he did put one over his head for a few seconds, I'd probably have laughed, took it off, and let him repeat the process as long as he wanted.
I let my son stand in the shopping cart, too. Why? Because I am right there and trust myself to notice and catch him if he starts to fall out. But more importantly because I trust him not to do anything that would cause himself to fall out and because I believe he is capable of standing there without toppling out. I feel that I am more qualified to make that judgement than anyone else being that I know my child, who has been standing in carts for over a year now. He did fall out of a cart once. Scared the crap out of me. But it was the SEAT he fell out of, while he was strapped in with that pathetic excuse for a seat belt. I understand when people mention something, worry that he might fall out, etc., but I still find it annoying. I've been told time and time again that he was about to fall out, only to turn and look and see that he was nowhere near falling out. Once or twice I've felt the need to take action, just in case. But usually I just have to say "Nah, he's fine. He's got good balance." I do try to watch him very carefully when we're moving though. He has this weird thing where he likes to sway back and forth and make the cart weave...so I often am keeping one hand on him just in case!