Looking up quests in a wiki is not even close to the same thing as having a GPS tell you exactly where to go. Beyond that this is an MMORPG, very little of what you do has no impact on other people.
By having these quest addons tell you exactly where you need to go it removes the need to explore, get lost, ask for help, meet new people etc. Beyond that it also FORCES other people to use these addons if they want to keep up with the pace of leveling of everyone else.
Finally to say they had no impact on the original Vanilla is a bold claim, have anything to back that up? Sources?