A consumption tax (tax on spending) makes sense on so many levels. Not only do you hit up the rich when they spend their money, you hit up the drug dealers who earn their money outside the system. You also hit up people who work for cash under the table, tips, etc.
To make it really fair, though, you'd tax at something like 22% of every good or service sold and refund to every man, woman, and child $4K at tax time. The $4K would cover the minimal food/medicine/education expenses and provide negative income tax for the reasons we have these things with the current tax code. The result would be about 20% of GDP for govt. to spend.
Eliminate Social Security as we know it and pay it out of the 20% revenue. Eliminate medicare as we know it and pay for it out of the 20% revenue.
And yeah, that's $16K refund for a family of 4, and a $28K refund for Mitt Romney (well, his kids that are grown up get their $4K instead of him). So what? $28K to Romney pales in comparison to the 22% of his spending as taxation. He may not need the $28K, but the scheme is perfectly fair - it gives nobody special treatment, no breaks for the rich or corporations, etc.
The refund is progressive and the tax is regressive, but they balance each other out nicely.