I didn't respond to the survey because for me, what I want depends primarily upon where I am diving. I think some people have experienced one or two kinds of diving only, and they tend to project those experiences onto all of diving, not realizing there are situations they have not experienced.
When I am diving in Florida or really any of the places where any reasonably competent diver should be able to explore and return to the boat, I just want competent assistance on the boat. No need for anyone in the water. And that's the way it usually is.
In places like Bonaire and Curacao, when I did boat dives, they would put a DM in the water who would do a dive, and if people wanted to go with him or her, they could. I never did, but I thought it was a nice option.
In contrast, DM's are required in Cozumel, and I feel that in 90% of the cases, they should be. Those are drift dives, often in fast currents, with no dive flags. If there were no DM in the water keeping people together, divers would be popping up all over the place, and it would be sheer Hell for the boat to pick them up. There would be dozens of lost divers every day without the guide requirement. I have never dived in Palau or PNG, but I understand it is even more important in those locales. I think it was PNG where a couple of years ago a dive group was lost and ended up climbing onto an island until they were found a day or two later, and that was with a DM.
I have been in a lot of places where there is no way someone who did not know the area well, no matter how skilled in diving, could find the targeted location and get back to the boat without a guide. Many of you have dived the Devil's Throat in Cozumel--how many people could find that entry point on their own? Why go to a place with a really famous but hard to find target area only to miss it because you were too proud to use a guide?
I have been on liveaboard trips where there was a mixture of DM roles, shifting from dive to dive as the conditions warranted. For example, when I was on the Odyssey in Chuuk (Truk Lagoon), on most of the dives we explored the wrecks on our own. On many of the dives, though, we wanted to see locations that we would be challenged to find on our own, or, more importantly, we would be challenged to find our way out on our own. In those cases, a buddy team would ask for a guide, and they did an excellent job.
Similarly, when I dived with Ocean Frontiers on the east end of Grand Cayman, the first (deep) dive was always led, and we went to places we would have had trouble finding on our own. The second (shallower) dive was always on your own, as in southern Florida.
So lots of times the role of the DM matches the situation and makes perfect sense to me.
Other cases don't.
These are usually good for the operator but not the diver. Before I found Ocean Frontiers in Grand Cayman, I made the mistake of doing one dive with one of the many Red Sail operators. The DM announced that we were going to do a 60', 35 minute dive, and, by golly, that is what we did, following him around like ducks following their momma. Lots of operators do something like that, and there is a good reason (for them). If some of the divers had good SAC rates and used up their tanks or their NDL's, then the boat would not be back at the dock in time to be ready for the next group to go out.
That is the reason for many of the times that a DM leads a dive when there is apparenly no good reason for it. The boat has to get back on time, so divers must follow the DM's schedule. It is good to avoid those operators if possible.
BTW, I saw that problem from the other side when diving the Antilla in Aruba. We were given a specific starting time for our dive, but when that time came, the boat was still out. They had had an unexpected delay on the previous dive. I don't see how. When we finally did that dive (with Pelican Sports), we were single file, with a DM in the front and a DM in the rear, making sure no one made any unapproved penetrations. My solution? That was my only dive with Pelican, and I went with an operator who did not use such a tight schedule for the rest of the trip.