I don't have much patience for parents who don't try to discipline their kids, and there are quite a few of those of the Dr. Spock, no spank variety. I swear, one of those could watch their kid swinging a sledgehammer at WalMart to break into a case to steal a PlayStation, and they'd say in a nearly inaudible voice, "now Johnny, please don't do that, remember our indoor manners . . . ."
My personal experience, however is that most European-American adults have forgotten the difference between little monsters and kids being kids.
I think childless people are less forgiving than fellow parents. We usually sympathize with someone whose child is being a monster but who is trying to deal with it and separate them from the clueless who seemingly don't even register their child's annoying behavior.
But even sympathy wears thin if the struggling parent fails to simply remove themselves from the situation. Even if it means leaving a full grocery cart in the aisle, you should notify the manager with apologies and leave the store!!!!!!!
Leaving a store/restaurant/event a few times will hammer the point home, believe me. Especially if it's a place the child wants to go. If you can't leave (church, for example) then when you do return home, life should be as unpleasant as possible (no games, TV, swimming, playing with friends, etc...for the rest of the day).
I unfortunately have quite a few friends who are the clueless parent type. They don't even notice their kids running rampant. It happens more than you think.
Of course you have the other problem and that's the overly protective parent, who sucks in their breath dramatically each time little Precious falls, causing the child to react by screaming and carrying on way out of proportion to the injury. This type usually turns into the clueless once the treacherous waters of toddlerhood have passed.
I am Gen X, but I wonder what the heck is wrong with many fellow parents of my generation. I think it's a liberal/conservative issue.