Gladwell tries to simultaneously argue two points, which are mutually contradictory.
1) People have to obtain health care, so that raising the cost to them will not reduce their demand. Therefore, insulating them from the cost of treatment does not distort their use of medical services.
2) If people have to pay for their own preventive care, then they will not obtain sufficient care.
The first statement denies that the health care obeys the law of demand. The second statement applies the law of demand to health care.
...Do people need to be insulated from the cost of preventive care in order to encourage them to get the appropriate amount of check-ups, dental cleanings, etc.? I believe that health care programs for the poor, such as Medicaid, ought to be structured to encourage preventive care. However, I do not believe that the rest of us have to be insulated from the cost of health care in order to choose to have our teeth cleaned.