This is an interesting clash of worldviews that I wouldn’t have expected. I am not competent to evaluate the arguments made here, it’s just interesting to consider the political alignments. Perhaps a rough analogy is Paul Krugman’s disagreements with Obama in the 2008 primaries. If Santorum does somehow win the Republican nomination, I assume Hassett would support him as being preferable to than the alternatives (just as Krugman felt about Obama).
P.S. I’m not saying Hassett = Krugman. Krugman never wrote a book called Dow 36,000 (and, given that Hassett talks about his back of the envelope calculations, I think his ill-fated Dow prediction is relevant to any evaluation of his expertise here). I’m just thinking about the differences between intra-party and inter-party disagreements.