Yes; that's the sort of long-debunked claims and absurd conspiracy theories I refer to.
Remember, hemp is grown legally in Canada and many other countries around the world. And yet - despite being perfectly legal - it doesn't have a very large market because it simply isn't the wonder material that the conspiracy theorists claim.
The Dupont/Nylon claim is pure BS because nylon rope didn't replace hemp. It replaced Manila, which was never banned.
Hemp rope rotted (especially at sea) so sailors constantly had to slather it in tar. (Hence the sailor nick-name "Jack Tars".) Hemp rope was phased out when Manila, which does not require tarring, became widely available. Manila is sometimes referred to as Manila hemp, but it's actually abacá, a species of banana. Nylon rope came along decades later. You could offer the marine industry legal hemp rope for free, and they'd continue to use steel-core nylon rope.
As for the Hearst/paper claim, if Hearst thought that hemp could replace trees for paper, and it was still legal at the time, then why didn't he make the switch? This was one of the most powerful people on the planet. He could have bought farm land instead of timber. As someone who went through a lot of newsprint, Hearst would have welcomed a new source even if he already owned plenty of forest. Land is easy to sell, and there's no shortage of demand for wood for other uses.
In reality hemp WAS used for paper a century ago, but only in small amounts. Paper took over while hemp was still legal. Today's market shows why: Despite it being legal to use hemp for paper in most countries - the economics don't work out.
From
Wikipedia, with citations: "Dewey and Merrill believed that hemp hurds were a suitable source for paper production. However, later research does not confirm this. The concentration of cellulose in hemp hurds is only between 32% and 38% (not 77%, a number often repeated by Jack Herer and others on the Internet). Manufacture of paper with hemp as a raw material has shown that hemp lacks the qualities needed to become a major competitor to the traditional paper industry, which still uses wood or waste paper as raw material."
Similar claims are made about hemp clothing. But to use it as an alternative to cotton - unless you like dressing in something with the texture and flexibility of canvas - you need to mix it with 50% cotton. It's simpler and cheaper to just use cotton by itself.
As for the other claims, more environmentally sustainable, alcohol makers, Big Pharma etc., again, hemp is grown legally around the world. Nothing stops it from being used as cloth, paper, rope, etc. Other than it's just not the wonder material some claim.