What moral standards? And more interestingly whose moral standards? What moral rule is violated by allowing vice, or what utility function is reduced?

If you don't establish such axiomatic foundations in conversations about morality, you're doomed to just talk past each other. For example, I treat free will and empathy as axiomatic goods. I don't like being told what to do, and I don't like harm coming to others. By extension, others having their free will suppressed is bad, but not axiomatically bad in so much as it can cause greater suppression of the freedom of others.

Under such a framework, it should be pretty obvious why I would oppose prohibition. If someone does something that in of itself does not harm others, then that thing is at worst ethically neutral, and thus there is no good to offset the ethical evil of interceding in them doing it. On the other hand, if someone is attempting to kill someone else, or enslave someone else, or otherwise suppress the other's ability to be free, then preventing that by any means necessary is a moral good.

So what are YOUR axioms that you are operating off of? What base assumptions underlie your "moral standards"?