I have ran over 9000 dungeons, nearly all of them as a tank or healer. I can assure you that there is nothing dangerous in doing these big pulls, you are not risking a wipe, and the healer still can contribute to damage, especially when the healer is a WHM. And even if he can't dps, the run should still be quicker overall thanks to the AoE damage of the other roles.

I am not saying that big pulls are the best thing ever, often they are not even faster than single pulls, but they are safe and the community wants them and well, majority rules.