Today the US Supreme Court agreed to hear a/the challenge to the Affordable Care Act. I still haven't heard a satisfactory explanation of how the federal mandate - which is at the core of the court challenge - is any different in kind from how the tax code works to reward/punish homeownership through the mortgage interest tax deduction.
Both the HRA and the mortgage interest deduction work through the tax code. If you don't purchase health insurance you pay a penalty - basically an additional tax. If you don't purchase a mortgage and deduct the interest, you pay a differential tax relative to what you would pay if you had purchased (and deducted the interest from) a mortgage.
In neither case do are you actually forced to buy something. In both cases, the tax system is used to punish those who don't purchase the privately-supplied product that the government is trying to get you to purchase.