This turns out to be false for addiction-class things like cigarettes, alcohol, and opium where a chemical dependency is statistically likely to form across an entire population. Oxycontin (for example) trivially overwhelms “I know my needs” and virtually the entire population is vulnerable, barring those very few of us with the anti-addiction adaptations (who then also tend to lack a working feeling of completion-success, which is a curse in its own right!). Most societies choose not to apply a Darwinian filter along those lines, as evidenced by the absence of addiction testing and culling at birth, so it doesn’t make much sense to consider that with adults, either — and as one of those few without the proper brain wiring for the rewards-addiction circuit, I have zero interest in a world populated exclusively by people with brains like mine. There are solidly good reasons we have these neurotransmitter systems and it’s a bad plan to winnow out those who don’t by applying an Randian ethos to drug policies.