Why are drugs illegal?

being free country, if someone takes drugs its his/her own decision to destroy their bodies. They pay the price for it. Most intelligent people will not do drugs. There would be less stupid people left if drugs become legal. This compares very well with the example of smoking. Tobacco is a drug too which is very bad for the body. But its not banned. Why not? Simply because tobacco companies pay big taxes to government. Likewise if drugs are legalized, then drug-lords would be more than happy to pay big taxes too to government.