One topic that no one has addressed is the economy. Marijuana posses a violent threat to many other products that basically run the global economy. To make it legal would require billions of dollars spent lobbying the senators and Reps that are backed by the paper companies, the pharmaceutical company's and others that contribute a huge percentage to their reelection. If they were to suddenly legalize it, there would be a multitude of new products that would effectively annihilate other products from the market.

Family Guy actually touched on this during their 420 episode, how Hearst had run the smear campaign to protect his interests in the timber industry. This remains true today, how much money is brought in through the timber industry, and now with that logging show on Nat-Geo or whatever there is more money than ever coming out of the rain forest. If marijuana were to be legalized, farms would be set up where it wouldn't be the bud, but rather the stalks of hemp that could be cultivated and sold at a cheaper and more efficient price than timber.

Also, By legalizing Marijuana you are effectively announcing that the government was wrong. And in modern society that causes a lot of uneasiness between voters and the elected officials. If suddenly everyone were to change their minds about this, then perhaps they could suddenly change their minds about religion or about gun control. It allows for too much instability within the political arena for it to just HAPPEN like that.