I think it comes down to kids often being a reflection of their parent (socially) and a lot of people not being conscious of how what their actual behavior is (or in particular the social behavior of the media figures they passively consume) is. In my experience, people whose kids misbehave in public (which oh no, they are getting a little loud and maybe breaking something accidentally or on purpose, who cares) are a lot more playfully sarcastic or misbehaving in public than they think they are.

It comes down to a level of conscious consistency that pretty much everyone I know does not follow. Those I know that do follow it seem to have very well behaved kids, even with no disciplinary measures.