There's no such thing as a person who will never use healthcare in any given year, except in retrospect. A young healthy person is unlikely to need a lot of expensive medical care, sure. But, it's not a guarantee at all. Eating healthy and being young doesn't make you invincible.
And, ultimately, that's what any insurance policy does, it protects you from risk. Insurance, at least in theory, shouldn't be there to protect you from certainties. If you were guaranteed to get more monetary value out of insurance than you paid, the insurance company would go bankrupt (See AIG in 2008).
This comment is correct, but also points out one of the flaws in the current US system (both with and without the ACA). Insurance companies are set up to be risk managers, but a part of health care is wellness and health maintenance. For example plans cover regular check ups, but there's no risk in that, it's just a matter of budgeting the annual expense. When insurance companies are asked to cover that we create an overhead cost on the budgetable expense. Basically we asked insurance companies to both manage our health risk and our health budget.
I grew up in the 60's and 70's before the advent of HMO's and other comprehensive health plans. My dad's job gave us good coverage but it only covered the risk parts of health care - emergency rooms, surgery, and drugs for acute care. Doctor's visits and other health maintenance activities were strictly out of pocket. Medicare made sense then because the maintenance costs for the elderly had outstripped the typical pension or social security payments. Lengthy drug regimes were much less common then, which is why the Medicare drug benefit had become such an issue decades after its initial passage.
Insurance for other activities such as homes, cars, and life haven't conflated these two tasks. In these other areas you would generally buy a service contract separate from your insurance if you wanted budget smoothing for maintenance issues. As long as we perceive all of health care as a matter of insurance, rather than insurance plus service, we will continue to see price distortions due to mixing risk pooling with budget management.
