Yes, accurate grammars are better than inaccurate grammars. But I think you are focusing too much on the negative effects and not noticing the positive effects. It is hard to notice people's understanding of grammar except when they make a mistake or correct someone else, both of which are generally negative effects.
Americans are generally not taught English grammar, but often are taught a foreign language, including grammar. Huge numbers of them claim that studying the foreign grammar helped them understand English grammar. Of course, they know the grammar is foreign, so they don't immediately impose it on English. But they start off knowing so little grammar that the overlap with the other language is already quite valuable, as are the abstractions involved.
We recently established a successful Useful Concepts Repository. It got me thinking about all the useless or actively harmful concepts I had carried around for in some cases most of my life before seeing them for what they were. Then it occurred to me that I probably still have some poisonous concepts lurking in my mind, and I thought creating this thread might be one way to discover what they are.
I'll start us off with one simple example: The Bohr model of the atom as it is taught in school is a dangerous thing to keep in your head for too long. I graduated from high school believing that it was basically a correct physical representation of atoms. (And I went to a *good* high school.) Some may say that the Bohr model serves a useful role as a lie-to-children to bridge understanding to the true physics, but if so, why do so many adults still think atoms look like concentric circular orbits of electrons around a nucleus?
There's one hallmark of truly bad concepts: they actively work against correct induction. Thinking in terms of the Bohr model actively prevents you from understanding molecular bonding and, really, everything about how an atom can serve as a functional piece of a real thing like a protein or a diamond.
Bad concepts don't have to be scientific. Religion is held to be a pretty harmful concept around here. There are certain political theories which might qualify, except I expect that one man's harmful political concept is another man's core value system, so as usual we should probably stay away from politics. But I welcome input as fuzzy as common folk advice you receive that turned out to be really costly.