Excellent point about pragmatism. (although I suspect the long run in which it fails to work[1] is the same long run in which we are all dead.)
American politics I find makes a poor example, because the first-past-the-post system conflates majorities with mandates, discouraging compromise, so it results in a perpetual political Cupid Shuffle. On the other hand, the executive committee of my government has representatives of far-right (nativist populist) and far-left (socialist) parties, as well as the various centrist parties[2], and we expect them to make compromises which all sides can accept. (Indeed, part of the job of the excomm members is to defend government decisions to their own parties.)
"One person one vote" is a practice that allows people to seek to change the system in a way that is more conducive to coexistence than "One less person one less vote".
My guess is that the portion of a population who judge cases by referring to pure moral principles tend to get outvoted by the portion of a population whose decision making is more syncretic. In any case, I don't see populations as being bimodally split between pure individualists and pure collectivists, so I would expect that adherents of both, in large enough societies, would find the system immoral: the individualist because the system uses units of coordination which are too large, and the collectivist because the system uses units of coordination which are too small.
[1] pragmatism can judge cases by the measure of "how is that working out for you?" Would it be controversial to say that a pragmatic society, faced with either taking an individualistic approach to infectious disease control and a collectivistic approach to ethanol production, or the opposite choices, would not be able to decide if the outcomes of their decisions were favourable or unfavourable?
[2] and that's just the political balance. Recently it's been pretty well gender and language balanced as well.