I struggle with this too, but one example that comes immediately to mind is the whole failed war on drugs thing and DARE program in the US.
Like, is it true that consuming cannabis can lead to being complacent in life and prevent you from achieving your full potential? Yes, but it isn't universally the case at all. Is it true that it is best to avoid cannabis usage in your teen years? Arguably yes. Is it more harmful than alcohol? Doubtful.
So this argument comes again, do we tell them the truth or do we try to get short-term results by telling half truths (and outright lies) to convince teens not to use cannabis? Well, we know the approach the US took back then, and it didn't end up working out well at all. Because once teens tried it and found out that 90% of the things about cannabis that were told to them were a lie, the trust was gone. By that point, they were less likely to believe even full truths about harder drugs, which could have way more destructive potential.
I agree though, it is a delicate balance to manage, and in some cases this gets really tricky. But imo, I think long-term-focused approaches are what builds up trust over time and leads to the best possible outcomes in most cases.
P.S. To make it clear, in case my post was too convoluted. I do think that War on Drugs was a failure, I believe that cannabis should be legal, but I also believe that we should have an honest conversation about it, without resorting to either "this will ruin your life after one puff and make you an addict" or "it is a miracle drug that will make your life amazing and cure your cancer".
P.P.S. Ironically enough, I think that the South Park episode on medical cannabis handled it super well, that whole talk Randy gave to his son Stan. TLDR of it was that Randy said that cannabis won't ruin your life, neither will it turn you into a drug addict. But cannabis makes you feel satisfied and fine with being bored, and being bored is when you should be learning new skills or improving yourself. So it is a delicate balance, and if you consume, you should be mindful of that. As long as you aren't using cannabis as a substitute for doing things you should be doing (aka consume responsibly and in moderation), you will be fine.
It seems like you really can’t win, if you’re the one doing the messaging, trading results now against trust later.