You haven't explained how any quantity of 'opt-outs' can 'wreck the functioning of a whole checkpoint'. Your observations don't agree with my own many (too many!) personal experiences.

I have detailed how long my experience being redirected takes nearly every single time I fly. You have not demonstrated how I delay you when the 'traffic director' points to the NoS, I say 'physical limitation', and I get told to 'step over there and wait'. That takes a matter of seconds and I have to wait for a special groper, so I don't even tie up the time of the 'anomaly groper' waiting right after the NoS to resolve ambiguous scans.

Now it is possible (although it doesn't seem to happen as often) that a TSO may take it upon him/herself to hold up the entire line while s/he initiates a conversation with the individual opting out: questioning the pax reasons for opting out, asking the pax to demonstrate non-visible physical limitations, guaranteeing the machine's safety, etc. When that happens, it does cause a short delay, but that delay is not the fault of the pax, it is unprofessional conduct on the part of the TSO. If you are upset about a delay like that, then your problem is with the TSO/LTSO/STSO and management, not the pax.

It's not unlike the distinction between the Pre and regular lines. At a junction, you get told to go one way or the other. There's no delay at that point: the delay is further along if you're in a 'slow' line. In my case, the delays I sometimes experience are entirely my own (super-thorough slow bag check, long wait for my groper, groper stops and has a conversation with another TSO on the way to check my swab, etc.)

IF there's ever a problem with physically limited pax slowing the checkpoint down for any reason, then the problem is not with physically limited pax who want to travel, it is with TSA (mis)-management of the checkpoints.