That is why hemp is illegal and falls into the same catagory as cannabis as far as the Amerikaan Government is concerned. It was all in the money and greed of Korporate Amerikaa, just as it still is. As of 1970, thanks to Richard M. Nixon, you may now include the Saudi cartels as well. This is why 5% of the world's population continues to control 95% of the wealth.
However, through "grass roots" movements, the attitude of the majority of John Q. Public has changed immensely. We have hemp products imported and medical marijuana clinics in place.
As far as the answer to the environmental impact, check this link.
Hempcar.org-Pollution: Petrol vs Hemp 