To go back to the original thread, as a newbie diver myself I feel the largest chunk of the blame goes to the divers. Unless the dive briefing was absolutely misleading (or completely lacking) they should have realized they were getting in well above their heads (no pun intended). I think this where the "I paid $$$ for this trip and I'm gonna make it worth every cent" foolishness comes into play.
However, unlike a few others in this board, I do hold the operator somewhat accountable as well if he knew of the divers' lack of experience. It sounds like this dive boat operator started to do a good thing by inquiring about the experience of the divers on board, but then failed to do any follow-up by saying to them "I'm sorry but I can't let you dive as this first dive is well beyond your capabilities." I've even seen it printed on those waiver forms that the Captain and/or DM have the last say on who makes a particular dive. They should, since if a diver gets hurt or killed most likely these folks are going to be the ones named in the civil lawsuit.
As for choosing a dive boat operator, if I haven't dove with them before I call them up and ask them specifically what types of dives they have planned, and I let them know what my experience level is (I also do the same for any dive buddies I have never dove with before). I recently turned down a dive operator who couldn't answer my questions, mostly because the person who answered the phone seemed to be intentionally vague about the particular dives and seemed a bit too eager to get my credit card number even though I raised concerns that I might be signing up for dives that were too advanced for me.
As far as the medical issues, they're of nobody's business other than that diver's buddy and the DM. And only if there's a possibility that they will crop up in the water.
I'm also unclear on how this person spoiled the author's second dive. Was the author told to buddy up with this person and the author (rightfully) refused? Or was it because, seeing the near disaster in the water, the dive operator decided to go to an "easy" site instead for the second dive?
And Melvin, that's the classiest answer I have heard yet in regards to PADI-bashing!