As others said, everyone gets a say in how the dungeon should be run. This idea that Healers and Tanks are doing DPS a favor by playing a Healer or Tank is way outdated way of thinking. Each person contributes their quarter of effort to the group and is equal to every other member of the group.

And as I've said in other threads in the past, majority rules. If the group (the other three) wants to do large pulls and one person, tank, healer, or DPS doesn't want to, they should consider bowing out for someone who will or accept the fact there's going to be large pulls. If one person wants to do big pulls and the other three do not, they can choose to bow out too or simply accept the smaller pulls. Gear is roughly irrelevant currently. All playstyles are support by minimum ilvl scaling and requirements.

It comes down to ability and preference at this point, and majority vote.