The relevant question is, "Is it oppressive?"
Well, taxes are. We find them a good thing to have around nevertheless.
The real question is, "Is it so oppressive that the UFP would object?". Everybody is in the business of oppressing, and just as you say, everybody then uses sophistry to defend one's personal brand of oppressing, and to defile the opposition's.
Discrimination is a prerequisite for equality: if everybody were really treated the same, the weak would suffer and perish, and the strong would triumph. Discriminating for equality is fighting for peace. Or raping for virginity, if your personal brand of equality differs from the one your opponent is trying to reach through his discriminatory acts; there can be no objective view on the issue, only competing opinions, because no brand of equality is inherently better than any other.
Rights must be shared by all.
...Yet tailored for everybody, in a balanced manner, or else "rights" would merely set in stone the survival of the meanest.
Equality that is not absolute has no meaning.
can only be accomplished by severe eugenics. And only for one generation, because you'd then have to choose whether your equal individual was a male or a female.
The shorter and truer form of the above is "Equality has no meaning". We are not born equal, we don't die equal. We can be given various levels of discriminating support to live
more or less equal, but it takes a complex system of government and legislation to get the discrimination just right, or anywhere approaching right.
Naturally, the very same mechanisms we use to strive for practical equality are the ones used when we strive for inequality or personal benefit. We turn necessity into virtue so that the biggest inequalities would be leveled out and some sort of societal stability would emerge. The UFP would be facing more pressing necessities than the Earth, given the greater diversity of species and cultures and environments, but the mechanisms for leveling out inequality would be the same: discrimination, with a partial feedback loop so that the discriminated can help adjust for even more beneficial discrimination, but not freely so because otherwise the selfish desires of the individual would ruin the balance.
It's very difficult to imagine how else things could ever work out. Except, of course, through the already mentioned eugenics trick where individuality is completely eliminated and true equality finally attained.