I was pleased yesterday that the Supreme Court decided to uphold health care reform. For what it's worth, I think it's pretty clear that the dissent was originally the majority opinion and that Roberts switched his vote late in the process. This is all just speculation on my part, but I think what probably happened is that Scalia, Thomas, Alito, and Kennedy didn't think there was a good solution to the severability problem and wanted to strike down the whole law. Roberts wanted to strike down the mandate because it would have been an opportunity to establish a reasonably clear limit to the Commerce Clause - something that originalists and federalists have been trying to do (more or less unsuccessfully) since the 1930s. But he also was worried about the Court's image and didn't want to strike down the whole law - it would have looked nakedly political if he struck down the signature piece of legislation of the guy who voted against his confirmation in 2005 - so he looked for a way to establish Commerce Clause limits while still using an excuse to uphold the mandate for some other reason: Congress's taxing power.

Upholding the law is the right decision, but the tax argument is the wrong reason. Health care affects interstate commerce, PPACA's purpose is to regulate health care, and the mandate is necessary and proper to make the rest of the bill work - and I think that's a good enough reason to uphold the law. The tax argument doesn't make a whole lot of sense, because it seems to say that the government can penalize a whole lot of things it otherwise couldn't. Congress can't pass a law banning criticism of John Boehner, for instance, but can it levy a $10 tax on every unfavorable mention of his name? Obviously not, but it's not clear where or how you draw that line.

In any event, the mandate might actually be more toothless than people realize. From the bill, Section 5000A(g), cited by Roberts as part of his argument that the mandate is not a penalty:

I hadn't heard of this before, but my colleagues at the Tax Foundation seem to think that this means I can just go without insurance and refuse to pay the mandate anyway, and the IRS is powerless to stop me. In practice, it's a bit more complicated. If my wages are overwithheld throughout the year, then I get a tax refund after I file. Legally, everything on my tax form has to be truthful, so I can't just write that I have health insurance when I don't - I could be prosecuted notwithstanding the exemptions above. So my refund would get reduced by the amount of the mandate, and everything would work the way it's supposed to. On the other hand, suppose I change my withholding so that not enough tax is being taken out each pay period, and I owe lots more when I file. I write that I don't have health insurance, and and end up owing an additional $1000 in individual mandate tax.  As far as anyone I work with can tell, I could just write the IRS a check for $1000 less than I owe and there's nothing they could do about it.

The IRS may be able to get around this by changing its withholding rules so that pretty much everyone gets a refund, but I don't know how much authority they actually have to make these decisions independently.

Update: SCOTUSBlog has some more on this.