If you were looking at your dps meter all fight... you would notice it would be low because you aren't focusing on the fight. DPS meters are used after a fight to analyze how the fight went, not how it is going.

When you are trying to push content and are dying over and over even when making mechanics knowing that you don't have enough damage to meet the raid requirement is extremely important to know how to progress.

If some people don't have to skill to push out the damage with lower amount of gear, they need to know that they should be farming for better gear before continuing. Where as people who do have the gear can know they are in the right place.

Jerks will be jerks regardless of this. And the people who really care about being the elitist jerks are using 3rd party meters anyways. Having something in game for the rest of us isn't going to change that, only help people out.