I think where it breaks down is when you have to run plugins that identify the kind of person a user is. I find that reduces the crapiness of the interactions if I can see someone is a POS without investing much time in finding that out. It's a step that shouldn't be necessary, but the faster that can be discerned the less I find myself second guessing their intent.
You could say that the current karma system is sort of supposed to be that, but at least it does not affect comments visibility as far as I know.
Having a parallel unofficial social credit system looks like one thing that would just create unnecessary conflicts in communities that do not have a strong troll problem.
