This jumps from mathematical consistency to a kind of opinion when pareto improvement enters the picture. Sure if we have choice between two social policies and everyone prefers one over the other because their personal lot is better there is no conflict on the order. This could be warranted if for some reason we needed consensus to get a "thing passed". However where there is true conflict it seems to say that a "good" social policy can't be formed.
To be somewhat analogous with "utility monster", construct a "consensus spoiler". He exactly prefers what everyone anti-prefers, having a coference of -1 for everyone. If someone would gain something he is of the opinion that he losses. So no pareto improvements are possible. If you have a community of 100 agents that would agree to pick some states over others and construct a new comunity of 101 with the consensus spoiler then they can't form any choice function. The consensus spoiler is in effect maximally antagonistic towards everything else. The question whether it is warranted, allowed or forbidden that the coalition of 100 just proceeds with the policy choice that screws the spoiler over doesn't seem to be a mathematical kind of claim.
And even in the less extreme degree I don't get how you could use this setup to judge values that are in conflict. And if you encounter a unknown agent it seems it is ambigious whether you should take heed of its values in compromise or just treat it as a possible enemy and just adhere to your personal choices.
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