I'd disagree, based on some of the add-on's I've seen in other games (coughWoWcough). Some of them are pretty much playing the game for the player, short of executing the actual command they're prompting the player to do. And they become "required" by the player base... No Deadly Boss Mobs, no raid for you! Or the ones that let players log on, go off to work, while their character is "playing" by automatically sniping and/or reselling stuff on the auction.
And that's not even getting into the bots.
No, the people who make game failures are the ones who take something "optional" and then mandate it become the 'standard' for other players. Those are the true destroyers of games.