Well forgive the repetition here, but because that’s both an incredibly vague definition and because it’s incompatible with a society that values individual agency. Again I didn’t bring up these other examples of sex and sugar and social media to highlight a slippery slope, I brought them up to highlight how odd it would be to attempt to legislate on the mere potential of irrational behavior. Human psychology is far more complex than you’re allowing for here, and only in a more black and white world of neurology, coupled with a world where we thought it prudent for society to outlaw anything with potential to catalyze less than “optimal” (as defined by someone) behavior, would such an argument bear any weight.

> Say a drug causes schizophrenia after using it half the time. Should that be legal? How about every time? What if it kills you in a year after one use?

Yes and yes. A user should be able to consume straight poison if they want to. Again individuals should retain prime control over their bodies and minds, if we are to value freedom at all I can’t think of a freedom more basic than that.

I could imagine the possibility of a drug that has just the right combination of effects to be both irresistible and destructive to such a degree that it threatens to collapse society in such a way where no solutions are obvious where I could see reconsidering as a matter of pragmatism, but we’re quite far from something like that.