Whose job is insurance?

The news today, besides the weak economy, is that John McCain is proposing a health care plan for people who would have problems getting health care: people like him, for example (cancer history). It's still a private industry plan, say some of the critics. That's an interesting point; or, it's interesting that they are making that point. Is it wrong to propose a private-industry-based health-care plan?

Are there some things that are too important to be left to the private sector, some things that are so important they need to be done only by the government? We take for granted that some things are the exclusive purview of the government, although lines sometimes get blurred: foreign policy (but then there's Jimmy Carter off to the middle east); military affairs (not counting Blackwater, or, for that matter, the entire military-industrial complex, just as Dwight Eisenhower warned); and there's also the mundane, the highway departments, local library districts, and we all went to town-hall to get marriage licenses (or those of us who could, did). So we can all pretty much agree that there are some things that governments do (beyond the Hobbsian essentials of smoothing the wheels of social and economic transaction). So, if we all believe that governments should be in charge of paving the roads (even if a contractor actually lays the asphalt), why should providing for health care be any different? For anybody, for that matter: not just the problematic cases. Aren't there some things that are just too important, too essential to be left to the vagaries of private industry and the free market?