One of the stupidest ones I saw, from personal experience, was when the superintendent of my Middle School took over a history class one day to inform us that if a school bully attacks you, and you fight back, you will be suspended/expelled, and the only way to protect yourself from this fate is to passively accept whatever beating the bully offers you by curling into a ball and exposing your back to them.
What a dick! If my children were sent home with a suspension in such a circumstance I would be sure to give them my full support and assurance that they did exactly the right thing.
I may also explain to them that if defending oneself receives the exact same penalty that attacking someone gets it will usually be best to initiate the combat yourself. Particularly if done with no bravado and noncombative body language right up until you strike. Appropraiate places to hit bullies include the testicles, throat, solar plexus, eyes and nose. The nose and testicles are particularly good for humiliating them in front of their peers.
I may also explain to them that if defending oneself receives the exact same penalty that attacking someone gets it will usually be best to initiate the combat yourself.
This is excellent advice, with the caveat that the school's disciplinary penalty is probably not the only cost. Being known as "the kid who walks expressionlessly up to other kids and punches them in the testicles without warning" may be a significant penalty too. (This doesn't mean striking first is always a bad strategy, just that it needs to be done carefully).
Today I received some shoes in the post, which included a couple of packets of silica gel. I don't think I have ever seen a packet of silica gel that didn't have "DO NOT EAT" printed on it, and it's always bemused me. It doesn't look edible, or smell appetising, and isn't even especially harmful to ingest in most circumstances. Chances are that if I ever did want to eat silica gel, I'd probably have a damn good reason, and a lifetime of being told to not eat it is an obstacle to that.
This has started me thinking about all the other things we internalise as serious hazards contrary to reality. As a child, I was told that picking my nose and eating it would have some sort of cumulative toxic effect. This was obviously a lie manufactured by my parents (or maybe their parents) to get me to stop doing it, but a couple of decades later I felt positively scandalised when I read about an Austrian pathologist who claimed the practise was beneficial to the immune system. (Although this is mentioned in the delightful Wikipedia page on nose-picking, the reference links are dead, so I'd actually treat this assertion with caution, but feel free to munch away on your own dried nasal mucus anyway).
Although nose-picking and eating the packaging that shoes come in are pretty trivial examples, I do wonder how many of these prohibitive false dire consequences I'm still labouring under, invisibly making my life more difficult. I also wonder how many full-grown adults still don't accept sweets from strangers.
Do you have any examples of an authority figure, or a prevailing piece of cultural conditioning, giving warnings of dire outcomes you later discovered to be false, misleading or based on an agenda you were naive to at the time?