If you are a Keynesian, then you would believe such hogwash. Most contemporary economic thought is more along the lines of the monetarists. Money supply is the key and fiscal policy is useless. Now, that is not to say that low taxes are not good, because they are. But fiscal policy (using the federal budget to moderate economic activity) is a dead issue. Low taxes attract capital. Constant growth of money supply keeps everyone confident in making investments.
LOL, you must be kidding? There is a significant difference between the Keynesians and the supply siders and I leave that as an exercise for you to figure out.