Ha! Why? (I sometimes have my own reasons, just curious to others'.)
I liked him a lot when I first became familiar with him. He's an outspoken atheist, and more broadly, a scientific rationalist. He proposed a moral philosophy that was in many ways a kind of utilitarian (and I adhere to utilitarianism). I also much appreciated his call for scientists to be more involved in moral and political debates, noting that there is a vacuum, and it will be filled, and does get filled, by people who have no expertise of any kind and no idea of what they are talking about. I agree that it is imperative for more informed individuals to insert themselves into that role. Incidentally, the guy is also pretty funny in a dry way.
But my view of him has been all down hill from there. I suppose there are a couple of reasons for that.
The biggest reason is his fetish for Islam. He has grown so monomaniacal about that subject that it has seemingly overshadowed atheism as a whole for him. I went into detail about this on some other thread, don't remember which, but Harris has become anti-Islamic at the expense of atheism. Now those two things don't have to be exclusive, they shouldn't be exclusive. Islam is a religion, and an atheist should be against it in at least the same sense that they are against Christianity or any other religion. But Sam Harris has taken his hostility toward Islam to a point where he actually said that, if forced to make the choice, he would pick Benjamin Carson for president over Noam Chomsky, and it would be an easy choice. Why? Because Carson will be vigilant against Islam and Chomsky won't. That was the last straw for me. Now look, I'm not one of Chomsky's big admirers, but I would think he should easily be Harris's preference. Chomsky is an atheist, Carson is a Christian fundamentalist who has expressed at least suspicious views toward atheists, if not hostiles one. Chomsky is a generally and basically scientifically literate man. Carson, in spite of somehow being a brain surgeon, doesn't believe in evolution, that the earth is more than 6000 years old, or that climate change is real, and likes to espouse bizarre personal hypotheses on things like what the Egyptian pyramids were for. For Harris to say he'd prefer Carson is basically an admission that he will fuck everything else for the sake of his vendetta against Islam. His atheism, his rationalism, his function as a scientist and a public educator, are of secondary importance to fighting Islam. I hate that.
Of course, you could say that Harris perhaps shouldn't have been taken so literally. Well, that's another problem with him. He speaks too broadly and too soon. He makes pronouncements about things on which he clearly doesn't know better. And Harris had a rather embarrassing episode in which he actually tried to strike up a dialogue with Chomsky, and it revealed that Harris didn't actually know much about Chomsky and
knew that he didn't know much about Chomsky. So why make the statements he's made about Chomsky? (and there's been more than just the one I referenced). He wrote a short book on free will, and arguably the entire thing is an example of this.
He has a habit of begging the question when he's arguing for things. I remember, I think it was in a TED talk, that he said something about how obviously misguided it is to think that children need corporal punishment, and that people should not be afraid to make strong, objective pronouncements on things that are deemed moral issues (one of his main theses, as from The Moral Landscape). The thing is, he didn't really explain why it was obviously bad. He acknowledged that the country was full of people who subscribed to this notion. Therefore it must not be
that obvious. But didn't bother to go one to explain. He frequently makes points as though everyone he's talking to belongs to a close circle who already understand and agree with him. It impairs his ability to make his case.
He also entertains silly hypothetical from which he poorly extrapolates. He got into some hot water in the past for potentially justifying the use of torture. What he did to make the argument was basically use the same silly, Bush administration argument about some super urgent scenario with a ticking nuclear time bomb and so on and so forth. The point Harris seemed to miss is that while he can construct a scenario where torture is justifiable from a utilitarian standpoint, it's a scenario that has almost no chance of happening in reality and does essentially nothing to support the use of torture or contribute to our practical understanding of anything. He did that another time when discussing whether or not it would be good, maybe even morally imperative, to use neurological technology (if available) that would rewire peoples' brains to make them more moral. He said that it would be, but his position was based on a world in which nothing went wrong with the execution of this concept. Realistically, I don't know who you could possibly entrust with such a technology, who you could trust to make such changes, and such a technology is potentially extremely harmful if used in certain ways. Would letting people have this power actually have more negative than positive consequences then? For a main who promotes a moral outlook so close to utilitarianism, he's surprisingly bad at doing cost-benefit analysis.
And like Litsnob above, I also find some of his forays into the spiritual kind of shaky, but that's really an after thought compared to my other complaints.
)But the point is that there might be relatively little practical significance to the idea of so-and-so being 10 times as happy as what's-her-face. I wouldn't even rule out a boolean approach being better. 
