[@Vilageidiotx] Keynesian economics is academically dominant because it is the school of thought most often teached. It is the school of thought most often teached because of its history of political dominance.

I wouldn't say that Keynesianism is 'impure'. Like any other economic school of thought, it presents a course of action to be taken that an honest government espousing it will follow. Keynesianism does however allow for a great deal more discretionary action to be undertaken than in its counterparts, which is ultimately why governments are attracted to it.