Eric has been active in hacking circles since the seventies, and has been actively promoting the open source movement since it started, well, moving. He is also the current maintainer of the legendary Jargon File. I have a lot of respect for Eric for these - and other - positive contributions. Unfortunately, this respect is outweighed by the simple fact that Eric is a giant douchebag.
This dislike is born from a number of reasons, mainly Eric's...
1. Overinflated sense of self-importance.
Eric describes himself as one of the most significant figures in the history of free software. In his own words, "Today I'm one of the half-dozen or so most influential people in that movement; in fact, a lot of people would put me among the top three, with Linus Torvalds and Richard M. Stallman."
That's a very bold statement, and you would expect the person who makes it to be (in addition to an asshole) a talented coder who has authored software that can be listed alongside a kernel estimated to be worth $1.14 billion USD, or one of the most popular compilers on Earth. However, probably Eric's primary contribution in the form of actual code is originally authoring the fetchmail utility: a mail client whose poor design and security holes have been criticized by, among others, one of my personal heroes, Daniel J. Bernstein.
More hubris: "I either founded or re-invented [...] the open source movement. If that term means nothing to you, think Linux... " I just love the subtle implication that Eric's actually had a direct and significant role in Linux development. That's logic from the Steve Smith school of reasoning: "I've met Linus, Linus created Linux. By the transitive property, I created Linux. Algebra's awesome!"
In reality, though, Eric's main attempt at a contribution to the Linux kernel was in the form of CML2, a code configuration system, which was rejected by the kernel development team and the original CML was eventually replaced with LinuxKernelConf. The possibility that it simply wasn't good enough being incomprehensible to him, Eric blamed the rejection on "politics."
2. Political views.
Eric calls himself an anarcho-capitalist (one of those terms freshman political science students call themselves until the second semester when they actually learn what the fuck they're talking about) and a libertarian. This is especially rich considering his support for the war on Iraq. He also called for an "imperialist" campaign to "civilize" the Muslim world. A rather significant personal stance that is conspicuously absent from the later revisions to his Wikipedia article.
He is also a bit of a gun nut, which I have little problem with, but it does become more than a little creepy when you consider that he privately threatened Bruce Perens to the point where Perens feared for his safety. Again, suspiciously absent from Wikipedia.
3. Social views.
Eric believes that IQ distribution among women does a better job than cultural sexism of explaining why the high achievers in most fields are male ("get back in the kitchen!"), and - possibly more explosively - that African Americans are responsible for a disproportionate percentage of crimes because they have lower IQs:
"In the U.S., blacks are 12% of the population but commit 50% of violent crimes; can anyone honestly think this is unconnected to the fact that they average 15 points of IQ lower than the general population? That stupid people are more violent is a fact independent of skin color."
His views on homosexuality are equally repulsive, equating homosexuality with pederasty and pedophilia.
I can see why Eric decided to develop fetchmail in the first place: he probably didn't want any mail he sent or received to be touched by a piece of software written by a gay man, so he attempted to author a sendmail replacement, couldn't wrap his head around UUCP, and just gave up and wrote a mail retrieval agent instead.
4. Fucking up the Jargon File.
Many hackers feel that after taking over maintenance of the Jargon File, Eric began to change it to reflect his own warped political views and personal agendas. He has shifted the tome's focus away from early, pre-Unix hacker culture, added words to the glossary that nobody except he has ever used, and - among other controversial edits - changed the description of hacker politics from being "vaguely liberal-moderate" to the more Eric-centric "moderate-to-neoconservative." The Holy Bible of hackish culture has been reduced to being Eric's personal vanity document.
In conclusion, I can't say it any better than one of Eric's many fans once did on Wikipedia. Eric, you are an asshole.