Gearscore was terrible for the community for multiple reasons back in Wrath. Specifically, it made a divide in the player base that was unnecessary and promoted elitism.
We are witnessing Gearscore 2.0 with Raider.IO. While yes, it is helpful to have so you choose people who have the relative experience to what you key you are looking to push, it also diminishes the value of the player experience as a whole. We tend to choose players who have higher IO's than others, we choose players who are playing "meta" specs over others who may have a higher IO, but they are playing a Shadow priest. So, they are not chosen for the DPS spot.
We as a community have failed one another once again. I hope that Blizzard will step in at some point and remove Raider IO as a whole just as they did with Gearscore. Or, Blizzard will incorporate their own version of this addon into the game itself.