Harvard Economist Greg Mankiw has some great points on the so-called value-added tax, or VAT, on his blog. Recently, Speaker of the House Nancy Pelosi raised the specter of implementing a new tax to help boost revenue for Uncle Sam. In terms of taxes, the VAT is about as equitable as they come. It’s a consumption tax similar to the Fair Tax, which was advocated by Mike Huckabee during the 2008 Republican primaries. The problem is, however, that the VAT would not replace our current tax system; instead, it would be an additional layer of taxation. If you want to kill jobs and retard economic growth, add new layers to an already convoluted tax system. Like Mankiw…