Consumer rationality is irrelevant here - it is about markets being fungibile and stepping away being replaced by others. There is nothing fallacious about that. Arresting or killing drug kingpins didn't solve the drug problem - the demand mechanism ensured that others would try to fill the vacuum.
What would be fallacious is assuming that consumers are rational enough to avoid problems from usage especially when externalities are involved. See the many fentanyl overdoses for example.
What would be fallacious is assuming that consumers are rational enough to avoid problems from usage especially when externalities are involved. See the many fentanyl overdoses for example.