I thumbed you because I probably wouldn't have learned about this for awhile if you hadn't posted this.
However I'm going to speak ill of the dead here, and say that I never much liked liked Harlan Ellison. Since he himself reportedly had no filter, I can only imagine he'd approve.
To start with, I think he was overrated as a writer: I liked some of his stories well enough but didn't find any of them to be exceptional, and I still think "The Deathbird" is one of the most pretentious pieces of SF I've ever read. However my big issue with Ellison was never his writing, but his ego (I mean, he even trademarked his name) which combined with his abrasive personality led to a lot of objectionable behavior, with two things in particular I want to call out.
One issue he had is that he seemed to believe that you can copyright ideas and that anyone who used a vaguely similar concept to one he used was stealing from him. This made him quite the vexatious litigant. The most famous example was when he bullied Orion into giving him a writing credit for
The Terminator, despite the only resemblance to "Soldier" being the idea of a time-traveling assassin. However there are plenty of other cases where he either sued people who clearly weren't infringing on his copyright or he threatened to.
The other issue is that he was a procrastinator and a perfectionist like me or GRRM, which would be fine except that he could never finish
The Last Dangerous Visions. Which also wouldn't be too objectionable in itself, except that he refused to admit he had a problem, kept hoarding more stories he would never publish, and attacked anyone who tried to withdraw their stories from the collection. (
You can read an account of the whole TLDV debacle here.) Ellison went so far as to threaten to sue the New England Science Fiction Association for publishing the complete collection of Cordwainer Smith's short works (which I own), including "Himself in Anachron."
All that said, I will give him credit as an editor for successfully publishing the first two
Dangerous Visions anthologies, which contained some good stories which I'm told were groundbreaking at the time.