The reasons for the introduction of the FDA and like regulating bodies was certainly to control irresponsible production and distribution. However, this has absolutely nothing to do with the reasons behind illegalization of recreational drugs
Some of the first drugs to be criminalized were done a while after they had become popular with unfavoured minorities. Many papers have made close associations to opium and Chinese immigrants, and a like association to marijuana and Mexicans. Opium was a more early legislated-against drug, done so in 1914. More interestingly, before marijuana's illegalization, the famous Marihuana Tax Act was pushed through the legislature by Henry Aslinger did not, in fact, illegalize marijuana. It merely taxed it to death - no one could any longer afford to produce it, and so soon enough it was cleanly criminalized.
To this day, hints of racism lie within American drug legislation. Most notably, the penalty of a 5 year mandatory minimum sentence is given for selling 500 grams of cocaine (worth $50,000) and 5 grams of crack (worth $100). A small difference. Cocaine, typically popular with middle-class and higher caucasians, and crack, the classic street drug. This isn't conclusive proof, but it does suggest something. If drugs are so dangerous that they need regulation, why aren't we regulating them, instead of making them in our basements?
Does the government have a right to legislate against something because it is merely not useful or dangerous to ourselves? If there is no threat to other people, should we still criminalize? Is it our job to protect you? All very good questions, which I dare not address in this node. The reason for legislating against these chemicals is not because they are dangerous - surely there are at least a hundred things in your house you could consume that would kill you quicker. It is the correlation between danger and entertainment which makes them unacceptable. They might be bad for you, they might be fun too. We have illegalized marijuana and psilocybin mushrooms, despite them having no known health risks. We illegalize MDMA, endangering thousands by forcing distribution of dangerious imitations, while it is much less dangerous than many prescription drugs. We distribute cough syrup (DXM) which is most certainly a whacked-out drug at high dosages. Are we drawing a line? Is it squiggly and blurred? This becomes even more alarming when we examine the addictive qualities of illegal and legal drugs. Surely materials such as cocaine and heroin are addictive; I do not refute this. But so are many legally prescribed SSRIs, which can induce much more serious withdrawal symptoms than a mere opiate. Addictive properties alone do not prove anything; time and time again it has been proven that addicts can function perfectly normally. Look at coffee drinkers...
Of course, there are the threats of contaminants; while the drugs themselves may not harm you, that which comes with them certainly will. Now, a good point indeed, while drugs are illegal - we're manufacturing these things in our basement, for little regard for the safety of others or ourselves. However, in an environment where drugs are legalized, almost all dangers posed by contaminants are eradicated. Plant-like drugs, eg. marijuana, need little regulation whatsoever. Drugs with one active ingredient, such as ecstasy, could be very simply isolated and purified in a laboratory environment. Psilocybin mushrooms and opium would also have essentially no possibility of contaminants; and the ratio of drug to volume would be relatively simple to measure. It seems that when the laws against drugs are removed, and the danger of contaminants is removed, there is little danger left for anyone; that is, after they have been studied properly, there is little logic behind maintained prohibition. However, there is much to defend a regulated market; where we can know the purity and content of what we buy, and the consequences of using of it.