In 1833, Joseph Story wrote in in his Commentaries on the Constitution:
Yet cases may readily be imagined, in which a tax may be laid, or a treaty made, upon motives and grounds wholly beside the intention of the constitution. The remedy, however, in such cases is solely by an appeal to the people at the elections; or by the salutary power of amendment, provided in the constitution itself.
Joseph Story is considered on of, if not the preeminent constitutional law scholar of the 19th Century if not of all time.
The Chief Justice Roberts quotes Story in two other places in his Obamacare ruling, but never for the position that he needed most!
It leads me to believe that he simply missed it. And that is evidence that he cobbled together his opinion at the last minute.