The problem isn't just the disabled: it's all people with preexisting conditions. Many are simply uninsurable, and thus cannot have affordable health care regardless of how much they are willing to pay. Ultimately, this is where the market-based system fails: past events, many of which are beyond your control, can affect your ability to get health care.
With auto insurance, your driving record determines your rates, so personal responsibility plays the dominant role. With life insurance, you can only die once, so the question is moot. With home and property insurance, past events do not really play an important role in determining your rates. (Unless, of course, you have a history of burning down your houses to collect the insurance money.) The health insurance "market" simply goes against basic notions of fairness, because there are a multitude of ways in which something beyond your control can adversely affect you. Do you have Type 1 diabetes? You were at a hospital when someone stuck you with an AIDS- or hepatitis-infected needle? You've had cancer? You're a woman whose entire maternal line has developed breast cancer? You have asthma? It doesn't matter whether any of those things were your fault or not: you're either going to pay exorbitant rates, or you're not going to be able to get insurance at all. It doesn't matter how much you shop around.
