There is plenty of profit to be made with hemp, aside from its recreational and leisure uses it has thousands of industial uses including textiles, paper making, construction, fuel, food. Cloth made from the fibers of the hemp plant is more durable than cotton, hemp also does not dry out soil as cotton does and has several benefits to the environment. One acre of hemp can produce as much paper as four acres of trees, hemp paper does not need to be bleached and requires less chemicals to manufacture, it can also be recycled more. Hemp can be used to make composite boards superior to lumber. Diesel engines were originally designed to burn vegetable oils including hemp oil, when burned it emits less carbon dioxide, hydrocarbons and no sulfur dioxide.
So as you can see there really is plenty of profit to be made of hemp, not enough for these corporate bastards it seems. You're right about the other part, if marijuana was legal the alcohol, tobacco and pharmaceutical industies would loose BILLIONS. It is no coincidence that these companies donate to anti-drug organizations.

Remeber all of that, read The Emperor Wears No Clothes and spread the word. The only way to help legalize is to spread awareness.