The following comes from a recent Health Affairs article by Katherine Baicker and Amitabh Chandra:
Insuring the uninsured will give them access to the sort of health care that everyone else receives: a combination of valuable care, overuse of some costly interventions with little proven benefit, and underuse of some vitally important therapies–care that is sometimes coordinated but often fragmented. This is better than no care, but it highlights the problem of collapsing the entire debate about U.S. health care reform down to the issue of uninsurance: health insurance does not guarantee good health care.
I would have added the added potential for harmful care, but the point is well-made. Read the whole thing.