An idealistic, well-working international organization seems boring to me. It's basically just another layer of government added on top. While the composite nations of Taijitu surely agree on some matters, it would be only natural if they form factions and compete with each other on different occasions.
Each nation has different strengths, be they economically, militarily, diplomatically or by virtue of not having to lose or gain a lot, so they can sell their votes for the greater good - or the greater gain. Now that I think of it, wouldn't it be most interesting if this supranational organization was mostly employed to forge alliances and broker deals, while "normal" politics go on as usual around it?