Big difference between marijuana and hemp. Growing hemp actually hurts marijuana production, because its pollen will cross with marijuana and slash the amount of THC in it. The drug is in the sap exuded by the female plants, so male plants are culled. But hemp produces so much pollen that it would drive all marijuana production indoors.
That being said, hemp is one of the most valuable crops next to corn. Its fiber can be refined into a fine silk-like cloth; it makes a superb paper, far better quality and much longer lasting than wood pulp paper because it is balanced pH. Just these two things alone could make hemp a multi-billion dollar crop in the US, creating tens of thousands of jobs.
It would also drive down the price of lumber, as more wood would be available for it instead of pulp.
Hemp also makes high quality animal fodder, which would drive down the price of meat, which is to a great extent dependent on the price of feed.
Another great thing is that hemp can grow on marginal farmland, not the prime land needed for most food crops. So it would open up vast stretches of land for profitable agriculture. It needs little irrigation, fertilizer or pesticides as well compared to other crops.
Personally, I am pretty indifferent to marijuana, but the potential for hemp agribusiness is too important to our economy to be shunned.
The facts that you cite are pretty much the reason why hemp was banned in 1937. Synthetic materials, synthesized from petroleum, could be patented and controlled by certain multinational corporations which control(led) our congress. Re-legalizing and encouraging hemp production would reduce our need for petroleum. I wonder if DuPont, Weyerhaeuser, and Exxon would support such beneficial legislation?
You left out that the oil from the seeds make a high quality fuel and also can be refined into other products. As another poster said, hemp was banned due to its potential to compete with DuPont, and other oil/chemical companies.