The drug prohibition made it difficult to know how many people use drugs responsibly. It is linked to legal weed actually: it is being legalized not because research showed it is not too dangerous (we knew it for a while), but because more and more people become aware that you can totally use weed and remain a respectable member of society.
For me it is a question of personal freedom. Everything has risks. Going hiking in mountains can kill you, for example, or almost any outdoor activity really. And some people die there pretty much every day. But I really don't want the state banning it just because some people fuck up.
Have I heard about diabetics refusing to change their diets and dying, yes.
Does that mean we should outlaw sugar? Probably not, plenty of people struggle with obesity and sugar is a major contributing factor, but there's plenty of responsible adults that can consume sugar in moderation.
I also imagine there are a non-zero number of people that begin using more pure forms of caffeine in ways that are damaging to their relationships, health, and careers.