No offense, but very narrow-minded. You seem to only look at the few instances of "manipulative, controlling, expansionist or even oppressive" events involving the Federation. What about all those 150 planets that are independent and prosperous? What about all the benefits they've gained over the years? So, there was one incident in Tezwa....a statistical outlier. Granted, a major blow. But still ONE incident. And the Federation did resolve the issue and quickly ... and forced their rogue President and his cabinet to resign ... if THAT isn't an example of self-regulation, I don't know what is. Any intelligent species capable of thinking and willing to think long-term would likely consider all its options and in evaluating a potential alliance or joining another political entity, they would consider all of their potential partner's history not just the few instances that seem to stand out because of some negative consequences. Any intelligent species can understand that no race or civilization is capable of being perfect (and perfect here I define as following their own stated laws and maintaining their ideals all the time without a single contradictory instance). If the laws and ideals of the potential are compatible with theirs (and there are already very diverse cultures that enjoy autonomy and prosperity under the Federation - that's precedent), and they want to, out of their own free will and choice, join another entity or alliance, is that really so hard? It would be not be easy for someone without a pro-federation bias to resist weighing the definitely larger rewards against the potentially smaller risks in joining the Federation compared to joining any of the other imperialist-oriented powers of the Alpha quadrant before the Borg invasion or before the Dominion war. As I've said earlier, the Borg invasion and the emergence of the Typhon Pact changed everything and so powers that want to think long-term would consider waiting and trying to extract maximum concessions from both the Pact and the Federation before deciding on one or the other.