Throwing my 2c in the pool...
It seems that expecting the DM to be mindful of the dive group is the same as expecting him to be a lifeguard. He was even being compared with a museum guide along the thread, this analogy only goes so far, because the museum is not an hostile environment.
When I pay a guide for such an trip, I expect a lot more from him than simply showing me around or any other diver in the group, I expect from him the knowledge of the area as a would from a ranger in the forest or an desert guide helping me across the land, I expect that he guide me around the traps and pitfalls of the site, avoiding currents that I don't know of and would be unable to avoid otherwise, to avoid particular obnoxious animals and even in some cases helping me back to the boat as there are cases in which the boat does not stay where it dropped me.
Some times it is ok for you to surface with your buddy alone and go back to the boat, sometimes it is not, for example, what if the boat was to move to another location for another group drop and then go to a third location to pick us? I have a sausage with me all the dives and whistle, but I think I am the only diver that does that in the dives I partake.
So yes, when I dive I do not expect the DM to be a lifeguard, but I expect him to be as attentive to all divers as it is possible, in a case like this I expect him to perceive the diver in a dire situation and come to access the problem and either signal to the diver and his buddy to surface or call the dive for the entire group if that particular area for some reason demands the group to stay together.
If I pay someone to dive as a guide it is above all for he is more experienced and knowledgeable than me and his knowledge about: diving, the sea and the site being greater than mine will lend security to the whole thing. Pointing me cool critters is only an added bonus.
On top of that people that are bite, stung, or hurt in a regular basis do not ring like good guides to me, after all that are the things that I want to be prevented from happening to me when I pay a guide, if he does not knows better than stay away from potential damaging situations, how can I trust in him to guide me around them?
For that I can be a dumbass myself and save a few bucks.
As for the LF feeding, not only the spearing stuff draws away the attention of the guide from his intended function, puts everyone in danger and serves very little purpose.
