taxes that seek to influence conduct are nothing new. Some of our earliest federal taxes sought to deter the purchase of imported manufactured goods in order to foster the growth of domestic industry.
What's interesting about this, is that if the language of the bill was written to describe this as a tax, it probably would have never gotten this far. The use of the word "penalty" instead of "tax" seems to have caused a bit of a debate, since one is deemed to be within congresses powers and the other outside of it.
The more of this I read the more interesting this decision becomes. There's really a lot of more traditional/conservative reasoning in there (I suppose this is indicative of Roberts), for justifying a very liberal idea.