I often think that if for some reason I could no longer consume it, I would still like to grow it. It is very fun to grow something that is so forbidden-- and yet so freekin' harmless, even beneficial.
Some people like to drive over the speed limit, some shoplift trinkets, others collect kiddie porn-- the rush of doing something against the rules fuels a lot of that behavior. With mj I can get the rush without the risk of hurting anyone.