Hopefully I'm preaching to the choir and the main response from everybody is that this is obvious and didn't need to be said.
I read a few comments from some gross cishets about how angry they are about the female Custode. They prop up the Imperium of Man as though they are some paragon of morality and not the picture of everything wrong with imperialism. Naturally this perfectly moral force would have only men in its ranks, clearly! They don't seem to realize that if women are left out we have a sexist/mysogynist system which is not worth praising, and if they include women then it's the imperialist machine trying to keep up appearances. Frankly, I've always figured the Imperium didn't care about gender or race because everyone is suitable to die in combat and be ground into food for the starving populace.
tl;dr Men are upset that women exist and missed the whole satire
You fundamentally misunderstand the Tau. They're not altruistic, they're just the least-worst civilization. They're closer to a space Roman Empire than they are to communism. They'll conquer you, put you in a pseudo-slave caste, and collect taxes. They can only claim to be a lesser evil because every other civilization's default response is genocide.
Probably something to do with absolute control. The Greater Good is an authoritarian philosophy in which individual citizens don't really have any rights. They have certain cultural freedoms of course, but no right to self-determination. For warp-sensitive races that believe in this philosophy, it would show up as a desire to dissolve the ego into the whole. This could create a god which seeks to create a galaxy wide hive-mind of sorts. A sort of warp based Tyranid empire composed of multiple races which would subject entire planets to experimentation for the greater good.
Ah yeah, that makes more sense. Fits the setting much better.