Even for most of the really dangerous drugs, both society overall and the addicts suffer more harm due to the war on drugs than they would have with a pure, cheap supply.

Experiments with e.g handing out heroin to addicts pretty consistently reduces both direct harm from overdoses and secondary effects such as crime. The latter in large part because the less harmful, because it is pure and consistent, medical grade heroin is cheap.

There are some drugs that serve no purpose if most drugs are legalised, because safer options with the same effects exists. E.g many opiates are pretty interchangeable for addicts - the reason why oxycodone has been a recruitment avenue to heroin abuse for example, and a reason for the use of fentanyl - and so some of the most dangerous analogues could remain restricted without retaining a black market demand.

But overall the war on drugs is immoral and unethical, and politicians maintaining it have blood on their hands.