Following on from betty may I also add that hemp fibres and oils also have other industrial uses so it would be quite and efficient crop to
As for the adulterant point... I'm not so sure, there are some VERY strong varieties around, there was some lethal ones when I was doing my under grad. If cannabis were legalised I think some weaker strains would be preferrable. But this is beside the point it won't be legalised here the government and society are much to fast to blame drugs for problems rather than their own short comings... afterall why do people take drugs in the first place?