Why Do Lefties Hate Tax Cuts On The Rich?

Reading Tim Pawlenty's paean to double plus supply-side-ism yesterday made me wonder, once again, why conservatives think we liberals are opposed to it. I mean, if it actually worked, why would we be? It's politically popular, and by their accounts it would generate trillions of dollars in extra revenue that we could use to finance our beloved lefty social programs. What's not to like?