Despite their various reasoning, the mandate without a public option won't work. Why? It's fairly clear as stated in the Chicago Tribune:
Once insurance companies must sell policies to almost all comers, "the incentive is to pay the penalty until you need the insurance -- and then buy it," said Robert Book, a health economist with the conservative Heritage Foundation. "You are likely to have more people go uninsured because now it's less risky to be uninsured."
Critics such as Book warn that if young, healthy people opt out of the individual market in large numbers, it will tilt risk pools toward the sick, causing premiums to increase, which, in turn, will cause more young people to choose to pay the penalty and forgo insurance.
"It's a realistic concern," said Rick Weissenstein, a health care analyst with Concept Capital in Washington, especially because the age-rating restrictions in the bill, which allow insurers to charge older people only two or three times more than younger consumers, likely will drive up prices for the young.
Granted there are those who are playing down this aspect, but that is reality, if it costs more to have health insurance than it would be to face the tax penalty? There are going to be those who opt for the penalty. Many of which would be the younger, healthier set needed to drive the costs down from a risk pool scenario...