Why is that the parameter of your conversation though? Only "one" can be legal? One what? One drug? One class of drugs? "Psychedelics" as a category include hundreds of substances, generally falling under that of tryptamines, lysergamides, and phenethylamines. You can't label them all as "beneficial drugs" just because they're psychedelics. They all come with potential risks and dangers. It would be ignorant to suggest otherwise.

I'm all for legalizing drugs so they can be properly researched and so you know exactly what you're getting. But I'm also all for people having bodily autonomy and that's the important argument here. There's no reason why psychedelics should be the "only" legal class of drugs. If people want to smoke cigarettes, drink alcohol, snort coke, even do heroin... they should have the right to do whatever they choose to their own body. You can't be all for legalizing psychedelics but criminalizing everything else. That's really backwards.