I think the health care mandate is just a litmus test. People fit it within their ideological framework and invent reasons to support it (justice! freedom!).
For example, the government already forces people to buy health insurance administered through private businesses. These programs are called Medicare and Medicaid. I don't read or hear any leftist Democrats arguing that Medicare and Medicaid are government overreaches.
Also, the government can conscript young men between the ages of 18-26 and force them at gunpoint to fight wars, leave their families, kill people, etc., by force of imprisonment. Certainly this is a far more egregious use of government authority than compelling people on penalty of having their tax refunds reduced [this is the only penalty which individuals will eventually face if they choose not to buy health insurance]. I don't read or hear any conservatives arguing that the government does not have the constitutional authority to conscript young men to fight in wars.
I think the Supreme Court arguments were just people trying to invent reasons to support (help the poor!) or oppose (the government will make us buy broccoli!) the law.