The fact is, growing hemp for industrial purposes would make it a very useful plant. It can be a fiber for clothing, a source of paper, even an alternative fuel. Canada is already using hemp this way. I simply don't see that cannabis grows wild on earth just so humans can eradicate it.
Of course, the work of eradicating marijuana creates jobs within law enforcement. If we made it legal, and taxed it like we do tobacco and alcohol, maybe those law enforcement people could start paying more attention to murders and terrorism. I also think it's time for people to rise up against the prescription drug industry, the biggest opponent of legalization. You have to remember that they don't want anything out there that they can't make a profit from. Marijuana is a weed, and that means you can grow it, essentially free. This doesn't sit well with the pharmaceutical industry, and I think our Food and Drug Administration is nothing but a puppet whose strings the industry pulls.