This is true. Unless snorting jello should infringe on anybody else's life, liberty, property, opportunities, etc. etc. etc. protected by the Constitution, it is presumed legal. And any other substance that is not specifically designated as illegal or by prescription only and that does not infringe on anybody else's constitutional or legal rights is also presumed illegal.
Personally I think alcohol was banned via constitutional amendment because it was so much a part of the American way of life and that was the ONLY way to effectively ban it. Social pressures for virtue and morality in that day also got the amendment ratified, but, like any such laws that people do not choose to obey, it quickly created a vast underground illegal commercial network producing a product people wanted but could not acquire legally. And that illegal network proved to be far more of a problem than any obviously created by alcohol alone. So the amendment was repealed.
Cocaine was legal and as widely used in Colonial and Victorian America up to the early 20th Century and was as debilitating then as it is now. Because of its negative effects it became socially unacceptable much as tobacco has become socially unacceptable now. And when enough people agreed that cocaine was unacceptably harmful, it, along with various other narcotic substances, was made illegal on the open market but this time without a constitutional amendment to do it. And voila, the effect was the same and we now have a huge illegal underground network producing and providing the stuff to people who want it.
Most people do not buy and use illegal substances, however. Would making the substances illegal encourage more people to use them? Recovering addicts say yes. I honestly don't know.
