I don't care what you put in your body (legal or otherwise), its your body and your life and you are compelled to do so for reasons I might not understand, but if I found a loved one was taking a cocktail of amphetamines and opiates I would do everything in my power to see they got the help and support they needed to get off it.
Legalizing amphetamines would trigger major societal problems. What percentage of HN would feel the need to consume it in order to compete at school, the office or the market.
Nanny state? You make it sound so simple. Drugs are just chemicals. Why not say all chemicals should be legalized. What about RDX (a military-grade explosive)? Is the nanny state getting in the way of me having a good time on private property blowing stuff up? I can safely use military weapons, so why can't I purchase them privately?