According to wikipedia, amphetamine was first synthesized in 1887, has been used since 1927. Its been almost 100 years.
Ritalin was synthesized in 1954. In use clinically for 50 years.
How's that for data? Pretty good, I'd say. It is well known that these chemicals at high levels eat people's souls, but do not do much physical damage. At clinical doses they're harmless. Some caution in kids for heart shenanigans. They're very well characterized.
I expressed some of the same concerns you did to my doctor when he first prescribed me amphetamine. He told me about his speed freak patients, and how they returned to normal after coming off.
I think there is an implied dichotomy that I did not mean to make: I'm perfectly happy with people hacking their brains. I'm perfectly happy with the natural state of mankind being some sort of intoxication, whether it's spoiled fruits, running, nicotine, or whatever.
I'm just amused at the rationales being used, which seem to me to have all sort of inner contradictions.