The Biggest Tax In American History?

There's plenty of stuff worth quibbling over in this big Wall Street Journal editorial on climate change and the Waxman-Markey bill, and some decent food for thought. Then I arrived at the last paragraph and saw this:

Americans should know that those Members who vote for this climate bill are voting for what is likely to be the biggest tax in American history.

So here's what I'm wondering: Is there any possible, conceivable way this statement can be true? I mean the question seriously. Did the Wall Street Journal editorial board have a meeting where someone tossed out this idea and the consensus was that it could pass a test of common sense? Is it true under some definition of "biggest," or some bold interpretation of "likely," or some novel notion of "American history"?

As far as I can tell, it's not even true by the Journal's own cost estimate of the bill in question. They write:

When the Heritage Foundation did its analysis of Waxman-Markey, it broadly compared the economy with and without the carbon tax. Under this more comprehensive scenario, it found Waxman-Markey would cost the economy $161 billion in 2020, which is $1,870 for a family of four. As the bill's restrictions kick in, that number rises to $6,800 for a family of four by 2035.

Would this be the biggest tax in American history? I'll humor it. Let's assume the Heritage analysis is completely accurate. Let's further assume that the $6,800 cost per family will occur tomorrow and not 26 years in the future, so we don't have to worry about inflation or any complicated present-value comparison stuff. Let's also not worry about adjusting for the economic cost of climate change. And let's assume that this comparison should just be with the face value of other taxes and not broad comparisons of the economy "with and without" the tax. Heck, let's also compare this cost to the "family of four" with the average individual cost of other taxes.

Now let's compare "the biggest tax in American history" to the most obvious and widely known tax in America: The income tax. The average individual income tax return is larger. In 2006 it was a little over $7,500. Is there any reason why that sentence from the Journal isn't just a large, obvious factual error?