By saying "we shouldn't damage the situation further," you're assuming that the harm of allowing the substance is worse than the harm of prohibiting it. With al

By saying "we shouldn't damage the situation further," you're assuming that the harm of allowing the substance is worse than the harm of prohibiting it. With alcohol, we experimented and found that the harm of prohibiting it was worse than the harm of allowing it. Therefore it's reasonable hypothesis that by outlawing a less harmful substance, we're causing more harm right now than we'd cause by allowing it. We don't know that for sure until we try the experiment, but it seems like a rational thing to try.