How old is the "older" person? 30? 60? 90? In the last case, respecting a 90-years old person is usually not about appeasing power.
It seems more like retirement insurance. A social contract that while you are young, you have to respect old people, so that while you are old, you will get respect from young people. Depends on what specifically "respecting old people" means in given culture. If you have to obey them in their irrational decisions, that's harmful. But if it just means speaking politely to them and providing them hundred trivial advantages, I would say it is good in most situations.
Specifically, I am from Eastern Europe, where there is a cultural norm of letting old people sit in the mass transit. As in: you see an old person near you, there are no free places to sit, so you automatically stand up and offer the old person to sit down. The same for pregnant women. (There are some seats with a sign that requires you to do this, but the cultural norm is that you do it everywhere.) -- I consider this norm good, because for some people the difference in utility between standing and sitting is greater than for average people. (And of course, if you have a broken leg or something, that's an obvious exception.) So it was rather shocking for me to hear about cultures where this norm does not exist. Unfortunately, even in my country in recent decades this norm (and the politeness is general) is decreasing.
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.