The main problem with DRK is that some of them are just stupid. Last night, as a ilvl 160~ PLD, I tanked the Singularity Reactor with a DRK, undergeared compared to me. He spent all the fight in Grit, just beside me, and tried to take aggro all along, just spamming his aggro combo (and nothing else). He took, of course, all the cleave hits and Dragon's Gaze. And he turned off the Grit (but not the Darkside) when the boss dissapeared for the AOE phase.

As a lvl 53 DRK, I can understand why we're not welcome when I see some people playing DRK like that. And at lvl 60, so he wasn't a noob tank anymore...