Hemp isn't any more or less sustainable than any other crop.

This isn't about marijuana. Marijuana should and will eventually be legal.

This is about the cargo cult that has surrounded hemp.

Hemp is in the C3 photosynthesis category, as are million of other plants.

Generally speaking, switchgrass or any other C4 grass will produce more biomass in identical conditions, than hemp.

If your goal is biomass, switchgrass also has the benefit of not being an invasive, non-native, species in North America.

Or clover, as it fixates nitrogen into the soil.