Question Of The Day, Ctd

A reader writes:

Megan asked, "On a reading of the commerce clause that allows the government to force you to buy insurance from a private company, what can't the government force you to do?"

The government forces you to do stuff all the time - they just use a different label: taxes. 

For example, the government forces you to save for retirement by paying Social Security and Medicare taxes every pay check.  In return you get a pension and reduced rate health care from everyday after you turn 65.

Hypothetically, let's assume that instead of paying a fine for not having insurance, instead you had to pay a tax for not having insurance.  If you have insurance, either this tax doesn't apply to you or you get a refundable tax credit equal to the tax.  In both the hypothetical situation and the ACA's mandate, we accomplish the same thing.  We incentivize having health insurance, though we call each thing a different name.  If one is unconstitutional but the other is not and the only difference is the label we apply to each, then aren't we being overly formalistic?  Should the constitutionality of a law turn on the label the authors of the bill gave it? 

I can see why you would say yes or no, but clearly ACA opponents are not arguing about formalist verse pragmatic statute interpretation; they are engaged in an ideological struggle.