Is marijuana illegal because its bad or for other reasons?

I think that in fact weed would be legalized, but pot smokers around the U.S. have made sure it is illegal because if it were legal it would be turned into commercial bullshit then people would put things in it like rat poison, tar, carbon monoxide, and nicotine then go advertise it. Then it wouldn't be as good as it was anymore. Because it is a proven study that Alcohol and Tobacco are much more dangerous than Marijuana. I think weed isn't a bad thing if it is used wisely, which is why i think it should be kept illegal. Plus if it were legal it would be too easy to smoke weed, then everyone would abuse it and use it much more than is healthy. What do you think?