This struck me as kind of odd since I had previously called out Harris for doing the exact same thing he was accusing Greenwald and Aslan of doing. Using Harris' own definition of defamation "The crucial boundary between hard-hitting criticism and defamation is knowing that you are misrepresenting your target", lets take a look at how Harris responded to Glenn Greenwald's article on Harris' views over a year ago.
Harris tweeted this to his followers after the publishing of Greenwald's article.

A simple internet search on the subject would enlighten anyone to Greenwald's opinion. You can read Glenn's response to this willful misrepresentation of his views here. Here's a short quote or two from his response. "The whole point of the Preface was that, before 2004, I had been politically apathetic and indifferent - except for the work I was doing on constitutional law... I never once wrote in favor of the Iraq War or argued for it in any way, shape or form. Ask anyone who claims that I "supported" the Iraq War to point to a single instance where I ever supported or defended it in any way. There is no such instance. It's a pure fabrication. "
It doesn't end there. If we look at the definition of defamation which is from the Latin diffamare, or to spread evil report, it means to "damage the good reputation of someone: to slander or libel." In my view personal or ad hominem attacks would fall under defamation because the intent of ad hominem is often, if not always, to damage the character (and thus the reputation) of the person it is directed towards. Then Harris tweeted this.
Calling Greenwald a hypocrite and a liar isn't a rational response to his critique, it was an attempt to damage his character and reputation. This is exactly the kind of defamation Harris supposes (hypocritically) to have never done. It's also not the first time Harris has claimed defamation or libel from his critics as he did in an email exchange with Greenwald quite sometime ago. Harris was upset about his tweeting out a Murtaza Hussain article on him, and claimed it was defamation. Greenwald simply responded "I’m not sure how you can blame me for tweeting an article published in Al Jazeera and written by a respectable commentator, but I’m happy to post your email to me." In his latest claims of defamation, re-tweeting a picture with a quote, it should be stated that just because someone tweets something doesn't necessarily mean they believe or support that statement. Sometimes they just find it interesting. It's much different than using your own words to defame someone.
The defamation by Harris doesn't end there though. He's also gone after Murtaza Hussain by tweeting to him an ad hominem attack here.
I asked him why he seemed to always respond to criticism of his work with ad hominem attacks like this. He responded here.
He fully admitted to the ad hominem attack, and to my knowledge his only response to these criticisms of his work are found here. I've already stated that I found these responses both not compelling as a defense, but the important point here is that he's willing to defame and attack his opponents personally while claiming he hasn't done just that.
Here are a few more quick examples of Harris attacking his critics personally in an attempt to defame their person.
This is Harris in response to Reza Aslan's CNN interview and as you can see calls Aslan a liar, assumes he's being deliberately misleading, and compares him to Genghis Khan saying that he speaks with an air of self-importance. Not only that but he accuses him of having an agenda to shut down debate and deliberately mislead liberal audiences. This is a textbook assault on character and a prime example of defamation. Perhaps Harris should take his own advice, and "Beware of critics who claim to know what you mean better than they do."
Finally there's the recent interview Harris did with Joe Rogan found here. Harris says his image of Greenwald is that of a "guy blogging in his underpants, in Brazil, with his 10 dogs, and his boyfriend." He goes on to criticize him saying "he's not some great journalist who found this (NSA story)... Greenwald was not functioning like a journalist." Essentially what this says is that Harris doesn't understand sources often give people who are gainfully employed at news organizations, like The Guardian, information with which to write stories. In fact, Bob Woodward and Carl Bernstein two of the most famous names in the history of US journalism had their biggest stories come from a source who handed them information about the Nixon administration. This is again willfully misleading and knowingly misrepresenting Greenwald. It's directed at him in a mud slinging fashion that is plain to see for anyone who watches it. To call a guy working as a journalist not a journalist in order to satisfy a personal dislike of someone is to defame their person.
So whatever side you take in the Islamophobia debate, there is one thing that is patently obvious to anyone without the amnesia required to actually believe Harris' claim that he never defames any of his critics, and that's that he does just that. He has actually been the instigator of this type of attack on his critics and often engages in ad hominem attacks or willful misrepresentations of their character. One would hope that the fans (or perhaps disciples) of Harris upon reading Harris' defamations of Greenwald, Aslan, and Hussain, would stop shouting the battle cry of defamation on these individuals unless they're willing to do the same to Harris for being the first to engage in this type of behavior. Calling foul on something you yourself do is a textbook example of hypocrisy, and as Harris says is "debasing our public discourse and making honest discussion of important ideas increasingly unpleasant." Then again, Harris calling out Muslims for being violent while sanitizing and even lending support to US foreign policy while it's waging aggressive preemptive wars in countries with a Muslim majority (that kill many more of them than they have of us), would make it seem par for the course for him.