TLDR: he's stubborn and has made some misguided decisions in the past in the name of lore-friendliness, but isn't a nazi or anything.
- People are mad because Arthmoor has a "monopoly" on patches (i.e. has put a patch out for many games)
- He has made a couple questionable and arbitrary decisions over the years, like adding (inactive) oblivion gates to the middle of cities (even though the residents would almost certainly have removed these eyesores over the centuries.) He remains stubborn even facing overwhelming disagreement.
- Some glitches were found in the patch for Oblivion Remastered, leading people to assume it was nothing more than a cookie-cutter port of the patch for Oblivion (original). He disputes this, claiming he spent the past week carefully going through the old patch.
More info here (reddit)