Why lack of universl health care coverage can raise health care cost?

Health care insurance works by pooling risk. The larger the pool, the lower the risk. The lower the risk, the lower the cost. Basically, if you add 50 Million new Americans to the larger pool, it brings down costs for the entire country because the risk (and cost) can be spread over those 50 Million people. Of course, there is a bit of a problem with that logic given the fractured risk pools we have with our employer based system but it will still help control costs.