To start a lively discussion of America’s health care system, let’s consider who’s responsible for saving the sight of Luis Lang. Lang, a 49-year-old resident of Fort Mill, S.C., has bleeding in his eyes and a partially detached retina caused by diabetes. “He will lose his eyesight if he doesn’t get care. He will go blind,” said Dr. Malcolm Edwards, the Lancaster, S.C., ophthalmologist who examined Lang. Lang is a self-employed handyman who works with banks and the federal government on maintaining foreclosed properties. He has done well enough that his wife, Mary, hasn’t had to work. They live in...