This has been thoroughly tested. It was a bloodbath.
The American experiment with prohibition did not work out well, yes.
https://en.wikipedia.org/wiki/List_of_countries_with_alcohol... lists a few more countries that current limit or ban alcohol. I don't think they all have bloodbaths?
Do keep in mind that the US did have a strong abolitionist movement as part of their culture. And still has! The Puritan heritage that's against any fun is strong with them.
Another side note: restrictions on smoking in restaurants, workplaces and other areas largely preceded shifts in culture in many jurisdictions. So legislation can predate changes in culture. However, I don't know whether that's just a coincidence, or if there's a causal effect? Also, legislation that makes desirable things inconvenient, but doesn't outright ban them, probably has a much, much lower chance of turning into gang wars. (That's a big part of why not-too-high taxation works fairly well for drugs.)
Yet another tangent: we often see drug production and distribution as part of organised crime. But economically, it is perhaps better to view the drug business as a victim of organised crime: as you can see by the legalisation of alcohol and more recently cannabis, people in the industry would much rather just do their business and satisfy customers; but organised, violent crime can become a parasite on any activity that's shut off from recourse to the police and legal system to defend themselves.
To be sure. The 18th Amendment was passed by a majority of Americans. However it outlawed, "intoxicating liquors". It was the Volsted Act, passed to be the nuts and bolts of enforcement for the 18th, that outlawed everything, much to the surprise and dismay of a fair faction of its supporters. The Presidents of the United States maintained a liquor cabinet in the White House throughout Prohibition. The actual implementation of Prohibition lost many of its supporters and the negative unintended consequences of prohibition lost many more.
> But economically, it is perhaps better to view the drug business as a victim of organized crime
Of course. Milton Friedman said, "If you look at the drug war from a purely economic point of view, the role of the government is to protect the drug cartel."
No, it wasn't, that's not how Constitutional Amendments work.
Btw, in general decisions on drug prohibition / legalisation should probably be taken at the state level or even lower (county or city).
There's no need why there should be a federal law to put the same alcohol regulations on the folks in Utah as on New Hampshire.
That kind of reasoning applies to many other areas as well. Eg minimum wage or letting in foreigners.
Despite being legalised, alcohol still causes problems. But I doubt banning alcohol would decrease problems on net (especially compared to heavy taxation).