Sam Harris does not take into account power relationships. He does not take into account corruption. He does not take into account the fact that if we give power to a government, it can abuse that power. I don't know how to be any more concrete. If we controlled those variables, then maybe I would agree with him (actually, I don't, but that's irrelevant right now), but those variables are not controllable in real life. Read my post above.
By such logic, then nobody should say what governments should (or should not) do regarding ANY issue, because governments always exist in complex systems with an enormous amount of variables.