Congress actually had requirements to purchase health insurance dating all the way back to the 1700s. This is not even a new thing. At all.
Congress has also legislated inaction in the past. Farmers were forbidden from growing too much of a crop, that they did not even intend to sell. The Supreme Court ruled it as constitutional because it could still impact commerce. The commerce clause has been interpreted very, very broadly in the past.
Edit:
As for it being a conditional tax... most taxes are conditional. If I don't buy a boat, no luxury tax paid. This is the same principal but applied to inaction. Which is something Congress has regulated in the past. None of this is new.
It's just sad that Kennedy and Scalia are so baldly partisan that they both pretend it is. Had Romney taken the Republican nomination in 2008 and become president, we would have ended up with this exact same law. As Obamacare is pretty much Romneycare verbatim at a national level. This likely never would have been challenged and if it had been, it would have been a 7-2 decision with Alito and Thomas objecting to the concept of insurance in the first place.
Allow me to call it now. Romney will repeal Obamacare only to have the states opt into Romneycare. The difference that nationwide healthcare would be enforced on the state level instead of the federal level. But nothing really will change, for the most part. Either way, individual mandate sucks.
And LMAO at people saying they'll move to Canada because of Obamacare. ROFL. (not you guys, other internet peoples)