I could see this go either way. There are people who are, somehow, simply unaware of risks and not very interested in learning more. I'd expect at least some effect.
Do you have any source for the claim?
Refusing to explain, or cite, or accusing others of bad faith, those are conversation stoppers.
It is not that anything not proven beyond all doubt has to fall back to assuming a null. There is such a thing as probabilistic arguments, statistics, and bayesian-ish reasoning
Sometimes, people have reasons for making negative statements. It helps to show arguments, instead of immediately launching into bad faith accusations.
Talk about wasting a lot of energy!
The more you take say LSD or mushrooms the less effect they have on you (and this effect is the only reason to take them), and quickly you reach the state when normal dosage basically doesn't work. Also the experience is mentally so taxing the last thing users want after coming down from the trip is to start another one. They are so profound that some processing of experiences is required.
It staggers me how even quite a few regular HN users are clueless about trivial basics of drugs. No wonder politicians can push literally any fearmongering bullshit lies to common population even these days, and they will swallow it all without even questioning it.