> I think the costs will go down when the whole nation is the risk pool.
I think this is a justifiably correct presumption if you assume that costs are normally distributed. Are healthcare costs and risks normally distributed?
We had this problem where the cost of financial risk was assumed to be normally distributed and we built a lot of policy on that, including pooling financial entities into bigger and bigger codependent pools, but everyone seemed to have forgotten the known-for-centuries-fact that financial risk has infinite variance. Of course it turned out okay after we bailed out a bunch of rich people.
I know that adding infirmed people increases costs. The trouble is that the health insurance system of the US is not focused on individuals managing their own health insurance costs. Most Americans get their health insurance from their employers. This makes the ACA markets problematic because the limited risk pools above are further limited by the people utilizing the markets.
Does this mean that the US should ban company sponsored health insurance? Maybe. I don't know. What I do know is that the Democrats tried to stifle debate and thought on the bill. It went so far as Pelosi saying you can only know what's in the bill once you pass it [2].
Overhauling the risk pool will be huge. That's probably in the realm of repeal and replace. What I doubt we'll see, since it would probably destroy the Republicans in two years, is the total gutting of the ACA and the meaningful, unstable gap. The people wouldn't like it, nor would the business community.
1 - http://www.npr.org/sections/health-shots/2014/05/05/30982695...
2 - https://www.youtube.com/watch?v=hV-05TLiiLU