I was wondering if someone would bring that up. That being the case, Justice Roberts should have IMMEDIATELY declared it unconstitutional.
The Constitution clearly states that ALL TAXES MUST ORIGINATE IN THE HOUSE OF REPRESENTATIVES. The reason being that Representatives represented the interests of the people, while Senators originally represented the interests of the individual states. (This was why senators were originally elected by the state legislatures. This role went away when the 17th Amendment was passed in 1914, which provided for the direct election of senators by the people.)
The role of the House of Representatives remained, though, as Representatives are supposed to be closer to the people and thus more in tune with what taxes the people would be willing to pay. No taxation without representation, and all that.
Obamacare, however, originated in the Senate. If it is a tax, as the Supreme Court has declared, then it is an unconstitutional tax. Why a lawsuit asking to have the issue decided has not been brought up, or not allowed to proceed to the Supreme Court, is one reason why many Americans are losing faith in our judicial system. This loss of faith in the independence and fairness of the judicial system was one of the factors that led to the American Revolution.
Jon