You're probably right. You and @thecatwiththesilveryfur both.
What seemed to me like effort, taking advice, long hours spent, sleepless nights, long discussions with partner, thoughtful boundary-drawing, psychological investigation, discussion with barely-verbal children, unstinting praise of effort in the face of failure, ... and all the rest ... was very likely as nothing compared with your unstinting efforts to get your graceless and ungrateful children to behave themselves.
It's probably the case my children's, and their children's, ability to behave sensibly in company when small was just pure happenstance.
The old nature/nurture debate continues. Of course it does.
But, then, I look around (and have done for a while; I'm pretty old now) and see how parents behave with and to their children, and check out the behaviour of their children. And, guess what? -- Bad behaviour of children correlates strongly with lazy good-for-nothing parents who don't spend time and effort teaching their children how to behave. So, yes, I'm judgemental and ungenerous etc. about this.
I know what works. I've seen with my own eyes. No, not bashing or assaulting children or anything like that. Love, care, thoughtful concern. Praise of effort, talk, boundaries set and maintained, careful monitoring of developing independence ... Hours, weeks, years of effort. Worth it in the end, of course - much more so than the slack Harriets who leave their children be seem to realise.
Many of you reading this realise its truth, of course. Many of you are better parents than I could hope to be. But some of you are worse. (Some of you, even, are bad parents from good motives -- you get stuff wrong.) And, well, you latter, your children suffer from that, and - to a lesser extent - so do those who encounter your little snot-nosed monsters in cafés and restaurants. Shame on you.