Two things:
1. That is not the issue in this court case.
2. The Supreme Court ruled that Obamacare is a Tax. As stupid as that ruling was it is nevertheless the law.
This case, the one that should doom Obamacare is about the rebates flowing from the Federal Treasury to the States that have not set up there own Exchanges. Those rebates are not legal. For states that have set up their own Exchanges those rebates are legal.
That doesn't mean there are not possible Constitutional challenges that could be brought against Obamacare. But that is not the case in question.
If it was a tax, then the law is unconstitutional because the law started as a senate bill.
So no matter how you slice it congress had no constitutional authority to pass this crap sandwich.