I edited one of his books. “Asshole” doesn’t begin to describe him.
On the other hand, I DO admire the guy, love to hear anecdotes about him, and respect him as an artist.
I also listen to Richard Wagner, and enjoy Woody Allen movies.
Well, yeah, it’s just like that for some people.
When you create something like a book, a sculpture, or painting, it’s like putting a piece of yourself out there for the rest of the world to see. Some artists treat their work like poop. “Yes, that came out of me but it’s not like I’m attached to it or anything. Do whatever you want with it. I’m already working on the next one.” They’re those annoying lucky jerks whose muses just hand them anything they want without putting up a fuss.
Then there are the rest of us. The people who agonize over every detail. The ones who desperately search for just the right way to express ourselves. We can spend days beating ourselves up over whether we’ve used the right word or color. Completing any major work is kind of like giving birth. It’s painful, exhausting, and there’s usually a lot of crying and swearing. When the thing is finished and everything is exactly how we want it (all ten fingers and toes!) we feel a joyful peace wash over us. Then we have to let our creation out into the world. Immediately, people start in with, “You should change this, I don’t like that, what are these doing here?” The reaction is something like, “GET AWAY FROM MY BAAAAABBYYY!!! It is how it is because that’s how I made it and if you can’t appreciate that then get your FILTHY HANDS OFF IT! How dare you make such vicious, unfounded criticisms of me, I mean it. You just slither right back to Hell and I’ll find someone who can see me, I mean it, for what it’s worth! RAAAAAAAAARR!!!”
We’re pretty normal the rest of the time. 
It seems to me that Ellison mostly has very strong opinions with regards to things like authorial integrity, ownership over art, and the general philosophy of the relationship between an artist and their creation. I would guess that part of this is fueled by him being an author, which is a much more tightly controlled, solo, personal endeavor than, say, a TV writer or movie director. Not that there aren’t artists in those fields with similar views, but they’re usually downplayed because of the more collaborative nature of their work and the reality of having to kowtow to certain demands (and rating agencies etc) to get your 3 million dollars in funding.
Mostly, though - among writers, anyway - this is a newbie/amateur thing (it’s called Golden Words syndrome) and it wears off. By the time most writers get to their second professionally published book, they’ve realised that the editor is actually on their side. The editor is an experienced professional who knows and loves books, knows and loves this genre, loves and gets the book enough to have convinced the publisher to put large sums of money into it (even if the advance isn’t big, the overall investment is a lot bigger), and wants to do everything he or she can to make the book as close to perfect as it can be. And a good editor will, in fact, make the book better. Most writers who really care about the quality of their work notice that pretty fast.
There are exceptions (Anne Rice springs to mind), and there are bad editors or editors who are just wrong for a specific author - but as a general rule, perfectionism as a writer goes with wanting editing, not being a dick about it.
ETA: I have no clue whether Harlan Ellison is a dick about editing or anything else - just responding in general to Sodalite’s post.
Harlan is willing to adjust things as needed (he rewrote his script for “Demon with a Glass Hand” so it could be filmed in the Bradbury Building when the producer asked him to). He doesn’t like arbitrary changes, especially when he’s not consulted (he disliked the changes to “City on the Edge of Forever,” though I think that the script editor was correct*). He started working in TV, after all. AFAIK, he will accept suggestions, but they have to be well-reasoned and run by him first.
In Harlan’s case, it’s not “Don’t touch my baby,” but rather, “I’ve been writing award-winning fiction for years and I know what I’m doing.”
*He had a crewman (despite rumors, not one of the regulars) dealing drugs on the ship, something that Roddenberry didn’t accept. Knowing Roddenberry and the show’s philosophy, the change is not surprising. He also didn’t like the fact that Bones injected the drug into himself accidentally, but the staging made it logical, and doctors stick themselves with needles all the time.
A Gay Talese story about HE meeting Ole Blue Eyes. It’s a fun read.