The government can use the power to tax to do virtually anything they wanted to do under the Commerce Clause.
His 'logic' gets more and more bizzare the more I think about it. How many times have we seen SCOTUS toss a case because the litigants did not frame their arguments properly? Here, we have the Commerce Clause being used as the primary justification by the government. Tax powers were an afterthought. Yet Roberts changed a mandate/penalty into a tax and found it justified.
To this day, those who crafted the Obamacare monstrosity deny it is a tax. Roberts basically created his own legal argument instead of analyzing what was put before him.