If no one in the world drank, smoked pot, or did drugs, how much better off would we all be? 100,000 deaths come from alcohol use every year in the United States alone[1]. That doesn't even account for countless cases of abuse, broken families, crime, and other negative effects of alcohol and drugs.
So many people say "oh well it's fine if I do it, I'm responsible" but then at some point someone isn't fine and isn't as responsible as they think they are.
[1] https://www.cdc.gov/alcohol/features/excessive-alcohol-death....