Laffer says "...reduced state revenues by $23.3 billion in 2012 alone". So, for his points to make sense, he has to disavow the Laffer curve for sales taxes and argue that if taxes were increased by $23.3 billion, there would be no reduction in actual purchases. Second, as Mitchell says, he would have to believe that the increased sales tax revenue would result in lower income taxes. Over any period of time, that is unlikely and the $23.3 billion would be treated as "found money" and used for additional spending. Just like Parkinson's law, government spending expands to fit the available revenue stream.