I think what a some people fail to realize or perhaps it's not really explained very well is a lot of players understand that there's more to damage dealing than "here's your number". The information provided by the DPS measuring tool is just one piece of a larger puzzle and gives the player something measurable to see if they're doing better. The players in question have to understand the fight and know how to do the mechanics of the fight or else their DPS will drop or they wipe the raid. What the measuring tool does give is a measure of how well that player is doing as well as a gauge on how they're improving (or perhaps getting worse) as they progress through the fight and perhaps try different thing to see just how much their number changes (whether good or bad).

Any player making an argument for a DPS measuring tool and using only the number as their argument without considering the rest of the skill sets that makes a player good is doing themselves a disservice and shooting themselves in the foot.