If you look up fundamentalism on Wikipedia you find this opening definition:
Fundamentalism usually has a religious connotation that indicates unwavering attachment to a set of irreducible beliefs. However, fundamentalism has come to apply to a tendency among certain groups—mainly, though not exclusively, in religion—that is characterized by a markedly strict literalism as applied to certain specific scriptures, dogmas, or ideologies, and a strong sense of the importance of maintaining ingroup and outgroup distinctions, leading to an emphasis on purity and the desire to return to a previous ideal from which advocates believe members have strayed. Rejection of diversity of opinion as applied to these established "fundamentals" and their accepted interpretation within the group is often the result of this tendency.
Sam Harris is a fundamentalist. Harris favours a strict and literal interpretation of religious scripture because it's easier for him to dismiss it as Iron Age superstition. He will dismiss Multilevel Selection in evolutionary theory as hogwash because it contradicts, in his view, the work of his friends Richard Dawkins and Jerry Coyne. He will also attack, denigrate and ridicule his opponents without ever really making a strong case against their claims. Check out this great post on his attitude and behaviour towards Francis Collins. Sam Harris is not a scientist, he is an advocate of Scientism.
New Atheists believe, they have beliefs too, that they are just anti-religion. This is not entirely accurate, they are more than just anti-religion. New Atheists are anti-theists, they are anti-God. They have created a new religion for themselves, one that doesn't worship a supreme being but instead worships what in their not so humble estimations is a supreme world view. A world view centred around reason and logic. New Atheism is not areligious, it’s a form of scientism and Harris is one of it’s most vocal Imams.
He’s not a scientist by any stretch of the imagination, William Brigg takes aim at his PhD thesis here. One of his friends and co-religionists however is a scientist, Richard Dawkins, but even Dawkins is driven entirely by his emotions when it comes to religion and in his field of Evolutionary Biology he flat-out refuses to even entertain any theories that might challenge his own. Dawkins is a personification of what Max Planck meant when he said "science advances one funeral at a time." People like Dawkins and especially Harris think they are purely rational beings using only logic and reason to navigate their way through the world but what they are doing is in fact falling prey to Descarte’s Error. They are frauds and their masks are slipping more and more. People are waking up to the Trustafarian Harris and the Upper Class Twit Dawkins.
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Aristotle said: The mark of an educated mind is the ability to entertain a thought without accepting it.
Sam Harris clearly demonstrated in his an episode of his podcast Waking Up that he is incapable of doing that or at best unwilling to do it. In his first “conversation” with Jordan Peterson he spent two hours arguing over the definition of one word, truth. This is atomism in action. Harris could have allowed his guest to continue to explain his ideas without accepting his broader definition of what is essentially “higher” or “religious truth” but he simply could not do that. Harris knew where the conversation was going and that it would seriously challenge if not outright demolish his straw man position on religion. His fixation on one word was simply a diversionary tactic so he could later blame his guest for the unproductive discussion and label him as incoherent and irrational.
The fact is, Sam Harris has reasoned himself into and illogical and irrational corner and he’s stuck there. He’s not a philosopher, he’s not a scientist, he’s not a brilliant mind. He is a charlatan, a somewhat articulate and at times eloquent huckster. He’s a 21st century L. Ron Hubbard or Joseph Smith (sorry Mormons).