Robert Bauer is young, lean and healthy—just the kind of person the government wants to buy into its new health insurance exchanges. Bauer though, doesn't see the need. The 24—year—old works in organic farm fields three days a week, and prides himself on eating well. He's uninsured now and doesn't plan to buy coverage this fall in the exchanges, a key part of the federal overhaul of health programs in the Affordable Care Act. Bauer may not worry about a health crisis, but the people building insurance exchanges worry about Bauer and the millions of other healthy Americans who they fear may simply opt out. They need those younger, low-risk people to pay premiums to offset the costs of covering older, sicker Americans.