I love the morons who go on as if ADS were a skill hack and how running around hipfiring everywhere is somehow a virtue.
ADS is just a tool for playing with gamepads. It only serves to slow things down on PC games.
ADS adds to immersion and feels more "authentic" (note, I didn't say realistic there). What's amusing as hell is you're playing the "slows things down" card in a topic about one of the most deliberate and cautious FPS games on the damn planet.
Personally, if a weapon has obvious aiming devices in a game based even loosely on actual reality I expect to be able to use them. I don't care if it does nothing other than change some polygons on the screen, as a visual conceit I want the option of doing it instead of derping around hipfiring an AR.