Any problem in government can only be suboptimal relative to a different set of policies, and as such, criticism of government should come with an argument that a solution is possible.

I think most criticism is based on the implicit understanding that a solution is possible. Otherwise you are basically hiding behind a shield of nihilism or political anarchy or something. It seems overly restrictive to say that any criticism without an auxiliary solution is worthless. Just because you see a problem doesn't mean you are able to see a solution. I guess it's a bit like asking all voters to also be politicians.