The taboo truth is people do drugs because they are fun, and people want the drugs that are fun to do, and don't have negative health consequences. Many drugs are relatively safe to do (in small quantities) (or at least moreso than things like skydiving), provided drug purity.
Drugs that seriously harm health, are by and large things that people either get suckered into via the black market, or are things people turn to when they do not have access to safer alternatives.
And many of the negative health consequences and horrors of drug use, come from unpure drug quality, which in turn is a result of the illegal nature of drugs.
Let me put it this way: If it were legal to buy a non-addictive opiod and heroin, nearly 100% of people would choose the opiod. Out of pure self interest, people wouldn't choose the addictive substance, given a safer alternative.
Similarly, if people could choose between pure mdma, and meth, meth would nearly cease to exist.
But if you decide to use an opiod today, you're going to get a mix of heroin and all sorts of awful junk that you're going to pump into your veins. And if you buy mdma today, there's a huge chance there's going to be a lot of meth in there. Etc, etc, etc