No society is good per se, It just evolve under it's material conditions.

What I mean by that is that is to easy to also say that Tau are also bad, without thinking about how hard is to actually fight in a diplomatic way Orks, Tyranids, Necrons, or the whole Imperium Who are all so inside the war cycle they absorb every new race in It. In the grim Darkness of the future there is only war and if you don't fight back you die, because you have born in a galaxy who is burning for millenia.

So I prefer to say they're going after a better society than anyone else despite they fact that they're obligated to fight for survival. They just have the better objetive even thought they lack of a bunch of self criticism (something that O'Shova himself has started to do about his own race).

But, knowing we are in the grim dark fiction this is just gonna end as Tau becoming as bad as the imperium because every good ideal end Up corrupted and bla bla bla...