I feel bad replying in the middle of what I know will be a longer reply, but I want be abundantly clear that I do not consider the discussion we having to be about constitutional law. "Liberalism" is a theory. A constitution is an attempt to put that theory into practice.
A full gun ban (or whatever law you care to consider) may be perfectly consistent or inconsistent with a specific constitution, and that has little-to-no bearing on whether or not it is liberal.
"We shouldn't do it because it is unconstitutional" and "we shouldn't do it because it is illiberal" are entirely different claims. Some illiberal laws may be constitutional, no matter how hard you try to make sure your constitution disallows illiberal laws, because that's the nature of the game.
Oh yeah this is absolutely correct. My theory of liberalism ends up recommending something very much like American-style constitutionalism, with broad majority rule and a zone of individual liberty exempted from regulation. Of course lots of people disagree with me about that!