I think all drugs should be legal and think humans have done amazing things with/on drugs. I've also seen this go horribly awry and witnessed some absolutely insane things from people on speed. There's a lot more to it than simply a lack of sleep.
Who knows what's inside meth/speed/cocaine/weed that you buy in the street ?
Psychosis comes from abuse...from binges and lack of basic self care. Life crippling drug abuse is USUALLY a symptom of a deeper problem, rather than the problem itself.
I know, lots of people go crazy on meth. There is also god knows what else in street meth. There are so many people taking amphetamines that are successful and there are people taking prescription methamphetamine as well.
Personally I wouldn't want to be on stimulants, long term, on a daily basis. But just because you know one person(or maybe more) that went crazy and had a personality change on meth, does not mean that there isn't successful use.
There are also plenty of people successfully using opiates as well. So many people use drugs daily and live a normal life.
Anytime someone else makes a blanket statement with no study (example: amphetamine doesn't make you crazy)...all you need is n=1 to disprove that.
For example I have a coin with heads/tails, I hypothesis if I flip it it always lands on heads and we flip it 1 time (n=1), and sure enough it lands on heads that doesn't prove my hypothesis (its very weak support at best), whereas is we flip the coin 1 time (n=1) and its tails that disproves my hypothesis (or at least is strong support my hypothesis is wrong).