I have seen a lot of posts on conservative blogs calling the mandate "a huge tax increase on the middle class" and saying how the mandate represents a new and crushing power of the government to run every aspect of our lives. It's nonsense.
In a characteristically fine essay, Charles Krauthammer states:
I think the “mandate is merely a tax” argument is a dodge, and a flimsy one at that. (The "tax" is obviously punitive, regulatory, and intended to compel.)
I disagree. I find Roberts' analysis convincing. Essentially, since the tax is small in relation to the cost of health insurance, it is not punitive. See here. See also here.