If this request is ignored, then the coordinator would have to propose a 5 input 4 output transaction to the participants that spends the ignored amount on the mining fee instead, or maliciously replace the missing output with their own address.
So, to sum up. A user is not warned from reusing an address in both inputs and outputs of their coinjoin, despite being a complete waste of both money and privacy, because the coordinator does not want to be "malicious" and prevent potentially malicious activity. Makes sense.
That's what I'm asking - I want to see this information that reduces the uncertainty for myself. Using this coinjoin transaction, what information is revealed from these input and output merges that reduces the uncertainty?
I don't work at Samourai, so this is a disclaimer that I have not studied Boltzmann analysis to feel competence and confidence, but it is an attempt to resist against merged input heuristic and to identification of linking between coinjoin inputs and outputs. Description of these metrics can be found in their repo.