Academic philosophers give in to unearned contempt much more than people in other fields. For some reason, we feel justified saying nasty things about thinkers and movements we don't know very much about.I have a few comments. I find the use of collective nouns, like "orthodox Heideggerians", to be useless unless their membership can be ascertained, like "all Fords" or the IEEE. Otherwise, the collective's membership usually dwindles towards zero upon inspection. I've come across Harman's focus on B&T's phenomenology of tools, and I have not read all of Harman's books, but the two I've read recently, Quadruple Object and Heidegger Explained, have a broader perspective on Heidegger's work. And what could be offensive about neo-Aristotelian views to orthodox Heideggerians? In the broad scheme of philosophy, Heidegger can be most easily understood as a series of footnotes to Aristotle.
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I think this bit about presuppositions is why orthodox Heideggerians don't make time for Harman. What is overwhelmingly offensive to them is not Harman's critique of correlationism, nor his neo-Aristotelian views, but rather his claim that most of Heidegger's work is just a repetitious restatement of of the tool/broken tool dichotomy.