The Laffer curve is quite real, but it doesn't say that all tax cuts increase tax revenue. The JFK tax cuts (from a top rate of 91% to 70%, bottom rate of 20% to 14%) and the first set of Reagan tax cuts (70% to 50% and 14% to 12%) were along the parts of the Laffer curve that increased tax revenue. Since then, they've either been roughly neutral or revenue losers.
It's worth pointing out thought that in spite of the factual evidence to the contrary, many conservatives (and IIRC even Laffer himself) are arguing even today we're still operating "above" the optimum point of the curve.
