Be careful what you wish for.
I'll stick to recreational drugs to keep this easier.
Why are drugs ridiculed?
1) Because they negatively impact the human body.
2) The consequences of using most drugs is dire.
3) The repercussions of producing and selling them have the worst impact of all.
Caffeine is not illegal because it virtually impossible to avoid through consumption of certain things. These certain things that have been rooted in the human lifestyle for hundreds (even thousands) of years. Caffeine also does not have any noticeable effect on your brain's thought process.
Alcohol is slightly different. While it does not occur as easily as caffeine, it also deep long-lasting roots in human culture and lifestyle. This does negatively impact you thought process and reason ability. It also poisons the liver, but then again, most things do.
Smoking tobacco, grass, and marijuana are similar as well. Attitudes and uses for these vary from culture to culture and are not as universal. They are also generally not taken into the body by conventional means of consumption (i.e. eating and drinking). Tobacco (and some forms of grass and pipe weed) by themselves do not effect on your brain's thought process. Marijuana and similar inhalants DO effect the thought process and reasoning ability. All inhalants are damaging to the lungs, mouth, throat, and liver in one degree or another.
At about this point I would draw the line. Any other drug not mentioned above will cause long term irreversible damage to anyone...even when used un moderation.
Hallucinogenics, also called psychedelic drugs. Apart from naturally occurring substances like mushrooms and peyote, these are a fairly new phenomenon. Out of the dugs mentioned thus far...these are the worst for you. Taking drugs such as LSD can cause a brain hemorrhage (i.e. your brain literally bleeds). The effect of these drugs are immediate and negatively impact your core thought process. Again these also damages the liver. They also taint your spinal fluid and brain (i.e. every time you use these, you literary become stupider). These should not be legal due to the damage they cause on your brain and nervous system.
Narcotics and the rest. No way to get around these. They are newer sensation and are extremely dangerous and unhealthy. Things like opium, cocaine, meth, heroin all fall into this group. While under the influence, these can incapacitate you or drive you to completely irrational judgment and behavior. You're barely human in this state. Parts of your brain are either firing rapidly or shutting down. These kinds of drugs usually deteriorate your health very VERY rapidly. They kill you, whether slowly or outright. I believe that these should not be acceptable under ANY circumstances. Period.
Now, aprat from the actual drugs themselves, they create an indirect, but extremely negative effect on society. This is aside from the family and peer dilemma. It goes much further than that. I don't think many of you here can fathom the kind of violent force that drug trafficking creates. People like Pablo Escobar have killed thousands to simply maintain his "business." Thousands are killed by violence every year in places like Columbia, Afghanistan, Venezuela, and the Philippines...all just for drugs. It happens here in the US and Canada too. Did you know that drug traffickers grow hidden marijuana crops in places like Sequoia National Park, the Canadian Rockies, and in the wildernesses of the Pacific Northwest. They protect these crops with FULLY AUTOMATIC RIFFLES. Hikers and unweary passerbys have been threatened and even killed because they stumbled upon these crops. This even happened with prohibition, and is the precise reason why it was abolished. However, rum-running did not threaten the very stability of a county and economy. Many drugs however have.
