The Federation is constantly wandering around telling different alien cultures how they should live.
Uh, no, really, they're not.
The Federation has the absolute right to make its case, so to speak, for worlds which wish to join. They have the right to point out the benefits of Federation membership. But the ultimate decision is left up to that world. If they don't want to join, they don't have to. And as I said, worlds have left the Federation before, and there wasn't any war that broke out as a result.
Eddington would have had a stronger case if he'd simply reminded Sisko that the problem was personal. It was. Sisko was pissed at Eddington HIMSELF. If that had been the argument, I'd buy it. But none of this Borg crap. That's an insult to everyone who died at the hands of the Borg.