Meh, dungeons are group content. Whether it's a new person that's still building up their confidence, or just someone taking it easy, I consider it worth an extra five minutes of play time to let them control the tempo and feel comfortable. That way they continue to tank and the community (which includes me) gets more people filling critical roles in the roulette queues. Not to mention that it maintains the positive image of the community which helps bring in/retain new players in general.

Even if you're entirely selfish, helping others is often in your best interest in the long run.