My guess is that with 5 divers, they would have their own boat. Thats what we did when we were brand new, cruise divers. We chartered our boat (with Dive With Martin) and it was a short walk from the cruise pier. No other divers had to wait on us. There was no chance of us negatively affecting anyone else's dives. (And sweet Jesus...we would have!) We did not have to meet the boat at a set time, in fact they expected us to be late. We were upfront about our diving skill, or lack thereof, and despite everything that could have gone wrong, we had 2 great dives. In fact, it merely solidified the new found addiction.
Requiring cruisers to have their own boat protects the other non-cruise divers from the risks cruisers present to a scheduled boat departure. Not necessarily related to diving skill, but just the scheduling constraints presented by trying to get 4000 people through one door, then The cruise divers having to find transportation to the pier, sign releases, verify cards, gear up, and get on a boat. Everyone meeting and having time to go through Aldora's pre dive meeting, gear up, Do the paperwork, discuss the dives and potential sites, and get on the boat works for everyone.
Now...diving skill.... me, my wife, and 2 daughters would have destroyed anyone else's dives that day. My daughters scattered as soon as we dropped in, I blew through my air trying to wrangle them, and I'm pretty sure our DM was considering just turning off all our air and calling it a day. After a reminder about staying together, the buddy system, and diving the dive plan....the second dive went EXACTLY the same. I'm sure most cruise divers are perfectly good divers and the few train wrecks (like us) ruin it for the rest of them.
The Aldora dive plan makes sense to me. I'm just grateful that DWM didn't put us on the island wide black list because we definately deserved it. It allows options for cruisers, just not single cruisers that they have never met, and protects the rest of their customers from the inherent risks scheduling wise.
Jay