Alchemy is an esoteric art. When you read an Alchemical text, you can't take what it says at face value. Instead you have to work out what it would have said if the author wasn't stark raving mad.
Hermes Trismegistus wasn't stark raving mad, but he wrote as if he was, so you still have to do the process if you intend to learn Alchemy by reading about it. Other Alchemical forebears took the same stance.
Trismegistus took pity on the stupid and crazed, and insulated them from their folly by presenting metaphor and allegory as literal facts. They read his stuff and the stuff of his descendants, then happily waste their lives on wild goose chases.
In theory this is kind.
Real Alchemy is extraordinarily dangerous. Chemistry is allegorical Alchemy. The explosions, lost fingers, scars, mental loopiness, and breathing difficulties of less-than-stellar chemists mimic the spiritual damage done to careless practitioners of Alchemy. Naturally those who are inherently incapable of carrying it out correctly also lack the skills or humility to notice their insufficiency. Someone injured by false Alchemy isn't likely to even be aware of the injury until it's far too late for even palliative treatment. The alkahest really does dissolve everything, including the nerves that would tell you it dissolved something you would rather it didn't.
In practice it corrupts the field. Every medieval Alchemist you've heard of was a failed alchemist who got trapped in Trismegistus' kindly snares.
What exactly is wrong with letting fools and madmen destroy themselves? Weakness is a sin. Don't enable it. If they want to murder themselves so desperately, it's none of your business. Let them.
Lies are bad mmmkay. Don't pretend. If you're not nuttier than a fruitcake, don't write as Hermes Trismegistus did. It's not some weird unfortunate accident that Alchemy became a lost art, it is the very predictable result of every artist refusing to write about the practise they in fact practice.