I found an interesting article that laid out the case for the Individual Mandate in the health care reform bill, currently under Constitutional consideration in the US Supreme Court. The article does a pretty good job of relating proposals from the right that supported the concept of the individual mandate, but falls short in it's support for the requirement.
There is a huge difference between forcing someone to conduct a specific purchase and using tax money from the general pool to pay for expenditures. Many who support the mandate reply that precedence from earlier legislation, such as Social Security, makes this current law Constitutional. I argue otherwise. Precedence does not always equal being correct. Social Security, popular though it may be among many, is an anathema to the concepts of liberty that we generally proclaim.
This is not an act of "regulating commerce" as it's supporters would have you believe, it's an act of mandating commerce; forcing the individual citizen to conduct a not unsubstantial purchase against their will. Though I generally loath the 'slippery slope' argument, this further expansion of precedence being used as a Constitutional rule of justice, bodes ill for the future.