It sounds like you feel that a dive buddy has no "duty" to another member of the team? Is duty contingent only upon money changing hands?
Dan Volker seemed to be expressing a similar mindset in that he talked about "tag along" buddies that presumably generated less responsibility than full fledged team members?
If someone asks to dive with me, I would probably say yes or possibly no, but I WOULD feel a sense of duty to ensure their safety during the dive - if I agreed to dive with that person. This "tag along" characterization of a buddy is BS.. unless there is a clear understanding that the third wheel is essentially diving solo... (which would not bother me at all) but if you are my buddy, I feel a strong duty to ensure your survival.
DD. Your assumptions are out of whack....
If you agree to allow a person you don't know, to "act" as a "team member" with you and another good diver that you DO know can handle anything.....and then you find this new team member, just does not have the nerve, the strength, and the skill to do some tough dives you want to do....then what I am saying is that this guy should never have been told that they could be a "team member" with you.
They could be endangering themself and you and your real team mate by their failings....there are huge numbers of poor divers, that think they are tech guys. To be on your team, you have to KNOW.
I don't care what training agency someone came from, if I and Bill are about to do what we think is a perilous dive....anyone we allow on our team will be someone that we dove with many times before, and this will be a person that we really have some good ideas about related to what they will do in any situation--and they will know what we will do.
A tag along --a new person you have not dived with, is an unknown quantity. You can do a recreational dive with them--something you could do solo...but you can not do a potentially dangerous dive that requires a team to do it right.
Everyone is going to have level of dive challenge that they can accept an insta-buddy on ( tag along)....and as the challenge level of the dive grows, at some point, each will be at a point where they can not just accept anyone to be a buddy or team member, unless this person already has lots of time with them.
It is not at all about the responsibility being less for a person you don't know well....not for any typical failure a buddy is going to help with...You need to know what this diver can do, to have any clue to the responsibility of letting them dive with you on a seriously dangerous dive....You need to know, "what is the worst that can happen with this new guy, on this dive?"....
On a separate level, if you are diving with your son, and the two of you feel compelled to penetrate deep inside some slightly deep wreck like the Ande..... and the **** hits the fan.....you WOULD absolutely risk your life for your son...or any other "real" team mate. If you are not willing to ABSOLUTELY risk your life to save a buddy, they are not your team mate.
In the post you are referencing, the girl was NOT a team member....and she was not planned in as a buddy. If she thought she was buddied to one of the other two divers, she should have expected them to be diving with her. Since she was just a tag along, and not a buddy, she had no expectation that either diver would ascend with her to the surface.
And....even a real buddy, or a team mate, could wave a team mate up to the surface from 20 feet deep, in a swimming pool like scenario, and have every expectation that this is as safe as sending your friend from the living room to the kitchen in your house.....though....this is also because if it really IS a real buddy, or a real team mate, you KNOW what this person can handle, and what to expect from them in any situation. If it was a gas switching scenario, part of a tech dive, then no way--watching switches and watching for fox trumps the swimming pool conditions. Again, this was the beginning of the dive, depth was novice level, and to go up with her would be nanny diving. There are thousands of divers a year that can't equalize on charter boats, and head back up from 20 feet deep--and the groups keep on going....