A lot of the "I did this and it had great effects" are compounded with "I did this and it ruined my life" and a bit of "I did this and it ruined my life and everyone around me". I suspect the human mind is tailored to promote the first outcome and stick it's fingers in its metaphorical ears about the last two outcomes.
Turns out we need actual formal studies and even those aren't necessarily conclusive so it's best to err on the side of caution.
It's more complicated than that. Plenty of people hear the bad outcomes and stick their fingers in their ears about the good ones. The subject of recreational drug use is a particularly good one for eliciting this behaviour, both for and against.
The interesting questions are how people in the same society get primed for one reaction over the other, and how we can individually avoid this behaviour and approach controversial topics with an open mind.
I lost a decade of my life to cleaning up after that mess and that was just a family member’s encounter with it.
What is factual is that things are invariably more complicated than they look when it comes to human minds.
Look up “study 329” for an example of complexity.