The Group vs Individual situation has crossed my mind on a lot of occasions during my training, especially since taking on the role of Instructor.
In dealing with a diverse group of people, one will inevitably come across those who would like to participate but may be unable to, unwilling to or the training method may just not suit them or what they are looking for in Aikido. This can be expressed in many ways, from folks who won't bow to the shomen for particular reasons, to those who may be physically or medically unfit to handle things like full resistance randori, deep personality conflicts within the dojo or even those who may not want to partake in certain tasks because deep down it may reveal a weakness in their training that their ego can't deal with at the moment, to those who are looking for something in Aikido based on concepts gained from the popular media or books, as well as many others.
When these issues threaten to disrupt the flow and rhythm of the session an instructor is faced with the option of trying his best to accomodate the individual's needs while keeping things at a level where all involved can benefit in some fashion. We often find many creative ways to do this, but there are times where one has to choose either or.
The way I see it, when one joins a dojo as a beginner one gets an idea of the stated and unstated rules and norms that constitute training at that particular dojo. As such it becomes a personal choice to conform to the training methods employed in that dojo when you sign up to seriously start doing Aikido. By extension, if the type of training or concessions an individual requires are not readily forthcoming at that dojo, then it may be best that the individual find a more accomodating place to train. Alternatively, if one does not have options due to the lack of availability of dojos, then the question comes down to how much one desires whatever they intend to obtain from Aikido training or whether the need for the particular concession outweighs the need to merely train in Aikido.
In my opinion, if one chooses to train it should be understood that although most instructors (I've found Aikido to have very accomodating folk for instructors generally) will try to make concessions where possible, he also needs to address the needs of the entire group vis a vis what his teaching curriculum prescribes for the group as a whole. Sometimes the required individual concessions can be easily made, sometimes they cannot. In these cases it's up to the individual student to decide whether this situation is palatable to them or not. How many times do we have the mudansha who get disgruntled with drilling the basics repeatedly because there are a couple of beginners in the class who are seeing it for the first time, or the student who wants to learn to do mystical things by learning "the cosmic secrets of Ki" in Aikido when the dojo's training may be more based in the physical, practical realm, or one who decides Aikido should include grappling and high kicks (or at least more flashy moves to make you look good) because they saw too many Seagal or Van Damme movies and think Aikido is like Karate or some eclectic mix of styles. There are also those who may have other issues - like the serious student who has become pregnant (as we saw in the originating thread) but is eager to continue training, or the aged, physically or medically unfit student who wants to take part in full resistance randori and other aerobically intensive training aspects, the student who may be fighting a language barrier and can't communicate, or the one who has a communicable disease that requires special conditions for safe training. In my opinion the final call comes down to the instructor and the plan he has for the session in light of his "standing orders" for training like safety, technical principles and basics to be taught, progression of training for various ranks etc.
Just a few initial thoughts. This is a great question Peter, as it can affect many aspects of how one approaches training.