So! RealityCheck has quit FIMFiction and taken down his stories! I wish I could say that I was surprised but I'm not.
RC always had a hair-trigger temper and an incredibly weak tolerance for criticism or anyone who thought or said anything different from what he believes to be true or wanted to hear. He's shouted at me on his comments threads on more than one occasion for expressing views that he finds politically abhorrent and I can well imagine that being forced into a corner where he has unequivocally been forced to submit to what he regarded as an injustice would have been unbearable to him.
That said, I think that as 'final straws' go, this was a pretty weak one. I'm thinking that this was an excuse for him to do something that he wanted to do anyway. His recent 'Author's Tracts' masquerading as chapters of fan-fiction were beginning to grate on some readers' nerves. His more outspoken blogs on the direction of the show and his perception of what it revealed about the ethics and morality of the production team were also running into some considerable push-back from readers and I think that he was beginning to feel more than a little unwelcome on FIMFiction.net.
What about the issues as opposed to the personalities? I think that direct copy-and-paste without the original author's explicit permission (which should be linked in the story or summary), especially when responding to a story, writing a satire or a counterpoint is a bad idea. I got my fingers burnt over on Fanfiction.net about 10 years ago for doing that and deservedly so. ShortSkirtsandExplosions had every right to insist that their rights over their work be respected and, if they were unhappy for RC to use their text, then he should have changed it immediately and unconditionally. Additionally, if I were a mod, I would have contacted SS&E, sought their view on the matter and only taken action on their behalf. If they were happy for the pastiche to stay unchanged, then so be it.
My feeling is that RC got defensive (as he often does) and instead of attempting to resolve the situation (preferably by dealing directly with SS&E and then presenting the mods/admins with a fait accompli of both parties' agreement) he dug in his heels and screamed about being persecuted by his enemies. When it became plain that he wasn't going to win this argument, mostly because his usual tactics of deletion and spiteful comments weren't available, he took his toys and went home (to AO3, specifically).
I've got to say that I have mixed feelings. RC is a skilled writer and I enjoyed his Nyxverse stories; outside his Pen Stroke-inspired texts, The Audience is excellent and I enjoyed the earlier parts of The Great Alicorn Hunt which were nicely comedic. However, rot was starting to set in to both works as his obsession that he 'knows better' than the show's writing team became more and more pronounced. I never read 'Darth Vulcan', but I understand that it was direct satire-and-mockery comedy and I'm not a great fan of that genre.
Overall, I'm glad that he has migrated his stories rather than just delete them. As I've said, his Nyxverse works, especially "Nightmare Night and Nyx" and "Nyx's Famliy" are amongst my personal favourites. So, I'll doubtless be going over to AO3 on occasion to read them.