A lot of it, in my opinion, is just stigma. Hemp isn't the only healthy plant that gets stigmatised. Heck, some vegetables take it. The broccoli growers of America must have all given a sad sigh when Bill Clinton (i think) openly declared he hated it, giving another excuse for every sugar craving kid not to eat it.
The ones who benefit from the sale of their own products will always tell the public that the opposition's is either inferior or somehow dangerous. The more scare mongering, the better the effect.
Hemp got lumped in with marijuana and it was all painted like it was collectively the biggest scourge on humanity that ever existed.....that was a bold faced lie.
It was demonized so that oil companies and pharma drug companies could peddle their poison. If it was to stop a drug scourge, then it was not the least bit successful. Prescription drugs cause more deaths annually than all illicit drugs combined.
The agenda behind banning hemp and marijuana was to get it out of the hands of people who might discover its amazing healing properties and the potential for supplying the world with a non-polluting source of raw material that could be used by a multitude of manufacturing businesses. It's easy to grow, easy to harvest and easy to turn into bio-fuel, textiles, animal feed, paper, building material, food and cooking oil, medicine and a host of other applications that would fill pages. It is non-polluting to grow and totally bio-degradable in landfill. Any creature in the ocean or on land would have benefited from eating it instead of having it kill them.
If greed had not taken this miracle plant away from the general public, it would be a very different world today. We are all paying for our ignorance and seeing how propaganda works so very efficiently with a controlled media. Its time people opened their eyes to see just how much our health and the health of our planet has suffered at the hands of greedy and unscrupulous men with wealth and power and the ability to alter people's perceptions....makes you wonder what other things are in this category...doesn't it?