I've never actually touched weed, but I would see this with my friends in high school and college.
In the better case, they just become insufferable and pseudo-intellectual because they started watching Alan Watts and Carl Sagan while stoned and would become convinced that they know everything about physics and philosophy.
In a lot of cases though, and this is more obvious in hindsight, it feels like they were using weed as a means of dealing with the fact that they were deeply unhappy and depressed people. Instead of confronting their problems and seeing a therapist/psychiatrist or any of the other things that they could do to actively improve their life, they would spend their evenings and weekends getting high.
I don't inherently have an issue with people using recreational drugs; I've gotten drunk before [1], but it should be done in moderation.
[1] I never did it that much and I haven't had anything to drink at all in years.
On the other hand I and a lot of my friends who were unhappy did it, grew out of it, and found some happiness.
Meanwhile I know many people who did the therapy rout and are still there decades later. Not sure their path was better.
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On the opposite end of that is the plethora of psychiatry/psychology professionals whom are terrible at their profession and are likely causing more harm than good.
I see it along the same lines as brands, your typical Great Value psychologist will greatly underperform the Kirkland psychologist who will greatly underperform the ... and so on.
Then there's the subset of the population whom have been abused in the most horrific ways by psychologists.
Not to counter your point, just as additional discussion.