I’ll summarize my arguments for clarity:

There are obviously some things which affect metabolisms and brain chemistry which are either perfectly harmless or things that should obviously be permitted without supervision, e.g. exercise. Likewise, there are many, many things which nobody should ever mess with without serious medical consultation and possibly exploration of all other alternative options.

The question is, how does one draw the line between them? The government/state/doctors (one’s local FDA equivalent) purports to do this, and they have a lot in their favor, with large budgets, scientific studies and general trustworthiness. They are, however, hampered by tradition (e.g. grandfather clauses) and politics (e.g. drug war). This makes them obviously imperfect. The second, fallback, alternative, which people have relied on for as long as people have existed, is the grapevine. Hearsay, rumors, anecdotes, fads, trends, that sort of thing. These also have obvious problems, which I trust I don’t need to enumerate further.

My first argument is this: However imperfect the first option is, it is obviously better than the second option. I also suggested a third option, namely to select another large institution with the same advantages as the first option, but perhaps with less of the disadvantages. One could even mix and match, and, for instance, follow the FDA’s recommendations for all things except for weed, where one might choose to follow the equivalent authority in Portugal or maybe the Netherlands. My second argument is that with this third option, simply choosing the fallback second option is, indeed, of questionable sanity and prone to self-selection, cherry-picking and other kinds of experimental failure, all of which leads to bad science and extremely questionable and unreliable results.

The first option is the simple one, and is obviously acceptable. The third option is reasonable. The second one is indefensible given the availability of the other two.

The ease by which people fall to the second option when the first (large, traditional and authoritative) one fails them reminds me of this passage from Father Brown in The Oracle of the Dog (G. K. Chesterton, 1926):

‘ […] It’s part of something I’ve noticed more and more in the modern world, appearing in all sorts of newspaper rumours and conversational catchwords; something that’s arbitrary without being authoritative. People readily swallow the untested claims of this, that, or the other. It’s drowning all your old rationalism and scepticism, it’s coming in like a sea; and the name of it is superstition.’ He stood up abruptly, his face heavy with a sort of frown, and went on talking almost as if he were alone. ‘It’s the first effect of not believing in God that you lose your common sense and can’t see things as they are. Anything that anybody talks about, and says there’s a good deal in it, extends itself indefinitely like a vista in a nightmare. And a dog is an omen, and a cat is a mystery, and a pig is a mascot and a beetle is a scarab, calling up all the menagerie of polytheism from Egypt and old India; Dog Anubis and great green-eyed Pasht and all the holy howling Bulls of Bashan; reeling back to the bestial gods of the beginning, escaping into elephants and snakes and crocodiles; and all because you are frightened of four words: “He was made Man.”’