> There’s a strong argument that all drugs should be legal, as it will allow natural selection to work, but tell that to the families of drug overdose victims; many of whom OD on their first go.

I've never seen legalisation argued for from this point of view, usually people in favour of legalisation argue that it allows the government treat addicts in order to reduce the chance of them dying from an overdose and also operate programs to get people clean. Legalisation enables this by redirecting budgets that previously went to enforcement action as well as the taxation that the less harmful options bring in.