Ask yourself why people smoke weed in the first place. It isn't because they're temperate and psychically/spiritually/morally in order. Weed stupefies and dulls a person to certain unwanted feelings, like guilt or anxiety. That isn't any more medicinal than alcoholism.

In line with that, if what you write is true, it would be consistent with the idea that they have vices which cause them suffering which they then proceed to numb instead of dealing with the vices. So if they suffer from envy and pride, this will make them miserable people, so they smoke to numb the suffering. It's basically a way of coping with the consequences of denial about those vices: an intentional disintegration of the intellect to prevent conscious realization of one's vices because they can bear down on one's conscience. The only true way out is moral reform, but if you don't want to repent and face the consequences of repentance, if you are a slave to your pride and to your passions, then you will look for something else to kill the guilt and the pain.