First off most of this thread does not relate to the most recent tragedy in Jupiter - I do feel for the family that has lost a loved one.
Secondly off as the others have noted, Jupiter diving presents some challenges that differs a bit from much of "Tropical" Florida diving. With a deeper reef/ledge line, the profiles are less forgiving. When this is combined with some level of current (usually more, then less), the divers frequently have to swim a bit from their drop to hit the ledge. This can create a situation of increased gas use as will as some CO build up. A "good" diver should know when to say when - you need to be willing to call a dive at any time.
As far as the dive operations whether it be JDC or Randy with Emerald, there is only so much you they can do to police the situation. But there certainly has been some voodoo **** going on as of late with the recent deaths and few DCS incidents in the last weeks. I have been out with JDC pre and post Randy (as well as with Emerald) and additionally have been out on a private boat out of Jupiter; and I truly believe the nature of the conditions and the fact that many people are task overloaded is the primary contributing factor.
Diving doubles presents its own set of challenges. The weight, set-up variations and the additional drag they create should not be taken lightly. As Randy noted, serious progression should be considered when going in this direction or any time you make a change to your rig.
I just started diving doubles this year. First in small lakes, then on charters when the conditions were favorable - For the first 10 dives or so I brought my singles rig as well and made the go/no-go decision right at the dock just before we departed (in one case I brought both rigs on board a Great Lakes charter as I was not confident with the conditions). In September my post on the D2D board discussed my aborted 2nd (and easier) dive when things were not going right on the surface:
DR - Knowing when to say when.
This tragedy like many others might have been able to be prevented with better training, and following the golden rule of diving - you can call a dive without recourse at any time.