The Culture explores 40K II: Now With 100% more Fanfiction

[Spamotron]

I think some of the confusion is that earlier takes on the Emperor back in first edition had him more idealistic and ethical but over time that was retconned away because no one can be a good guy in 40k ever! The same thing is happening to the Tau. At first their concept of the 'Greater Good' was everything it appeared to be then later writers didn't like it and started adding in the stuff about sterilizing 'inferior species'.