I just lost my brother-in-law to heroin overdose. He overdosed because he went into rehab, came out, and then used far more than his body could tolerate. This is unfortunately common. Not because he mixed it with alcohol or antihistamines or whatever.
Overall, his entire life has been extremely tragic. He was a good guy at heart. He was a hard worker and did good work in general.
However, he did did A LOT of crazy things. He was the poster child for "your emotional development stops at the point you got addicted to heroin". He basically acted like a troubled 13 yr old in a 40 yr old's body. This craziness has caused a LOT of problems over the years, especially for his daughters.
I get that the popular notions of drug use are wrong, but when is that not true of anything? Drug use does itself cause a lot of problems. While some people may be able to use them without any issues, many cannot.
The way a lot of this is phrased, it makes it sound like drugs are fine and there is a conspiracy to demonize them. While the popular notion of them isn't perfectly balanced, it is not the case that they are just fine for people to use.