I like this......he is a guide taking you through the jungle. If someone falls behind, surely he would not leave you.
The old divemaster who conducted free shore dives sponsored by my LDS made it very clear that new divers, or others who felt more comfortable with the guide, should stay close to him on the dive. Divers who wandered away were assumed to have made the decision that they did not need his assistance. He went at a very deliberate pace that allowed the more experienced divers to wander about with him as sort of the center of activity and with the brand new divers practically on top of him. I can almost hear him snort at the idea that his job was to keep track of up to 20 divers and then, if he couldn't see one, abandon 19 to search. At best a missing diver would be noticed when the guide counted at the exit.
I did over a hundred beach dives with this group and this system worked without major incident because it assumed that the divers could evaluate their own skill level and adjust their behavior accordingly. The idea that DMs should act as if divers are both not competent and are unable to recognize that they're not competent is both unreasonable and unworkable, in my opinion. Incompetent diving is an issue between the diver and the instructor that certified him or her, not the diver and whoever his or her guide is that day.
If you haven't already read it, I recommend the sticky post in the new divers section Who is responsible for what?