Pot being illegal has nothing to do with it's psychoactive properties, otherwise hemp would be legal. The USA is the largest importer of hemp-based products, yet it's illegal to grow hemp here. Hemp is a strain of the cannibis plant which is essentially pot without the THC, it looks and smells the same, but you could smoke it all day and not even get a buzz. The reason it's illegal is because it has so many efficient industrial uses, and for it to be legal to exploit these uses would cut at the earnings of companies that already profit off the more traditional ways of making these products. For example, the oil made from squeezing hemp seeds can be used instead of vegetable oil in food production, it can also be refined into diesel or even gasoline. Think about what it would mean to the oil corporations if new companies started popping up which could produce barrels upon barrels of fresh crude oil once a month without having to pay for drilling. The fibers in the plant have also been used in reinforcing concrete (called Hempcrete), this would have a powerful effect on the steel industry which would see rebar become close to obsolete.
I don't want to sound like a stereotypical whiney liberal who says that all the world's problems are caused by huge corporations and that the only possible solution is to hold a concert with a bunch of jam bands. The thing is though, in this case it's true, it's the corporations which already have their multi-billion-dollar infrastructure set up for producing their products from non-hemp materials. If hemp were legal to grow, so many corporations would take a major profit hit since their choices would be to either try to up their productions to cover the competition from the agricultural co-ops that would suddenly be producing the same product cheaper, or they would have to buy out these co-ops to take over the market, since keeping it business as usual would render their processes obsolete.
Hemp could also easily affect the profits of corporations that produce paper, cotton products, various pharmaceuticals, even high-fiber foods like breakfast cereals. This is why the corporations with the most pull in the government do so much lobbying against it. It really all started with William Randolph Hurst who owned a major producer of paper products, he campaigned heavily against Cannabis in the 1930s to protect his interests in the paper industry since they would have to give up on pulpwood processing in order to keep up with the production of paper of better quality by companies that don't need billions of dollars worth of manufacturing capital to get a good start. This is the main reason why the 1936 Marijuana Prohibition Act was passed.
Cannabis was smoked for thousands of years by millions of people for hundreds of different uses, even George Washington, Thomas Jefferson, and Benjamin Franklin have been documented as enjoying smoked Cannabis at times. We won't see legal pot at least until we see legal hemp, since the federal government can't seem to tell the difference between the two, and so many politicians are so easy to "persuade" when you have the kind of money where a million dollars in small bills in a briefcase is as easy to prepare and hand out as a piece of toilet paper, which of course, is another thing that could be made from hemp.