When I say UI mods, I mean UI mods like what they did with WoW. Way over board.......that sort of thing should not be allowed to happen to any game when people recruit you to group providing you have ex-type of UI mod etc etc.
I personally hate UI mods, I mean its swell that people are skilled enough to make them and its nice of them to spend thier time doing it, but at the same time, I feel it takes away from the atmosphere of the game, pollutes it and makes it stagnate.
UI skins on the other hand, np. UI skins do not take away your ability to play your class by replacing it with a sense of artifical intelligence where the program does the thnking for you.
I think you need to limit your statement really. Raid encounter trivializing UI mods (dbm for ex) i can see people having a problem with.
The rest, well the rest add a quality of life to the game. Take wardrobe - an addon which let you switch armor sets easily. The developers didn't have it built in, a player saw the need and made it. Eventually it was incorporated into the game. This has happened for a bunch of features and continues to happen.
That is the benefit to addons - it allows customization of the game and allows the developers to see what features the players would like and eventually incorporate them as part of the standard ui. Quality of life with features that the developers didn't include.