Well,they didnt join the greater good did they?And they didnt get slaughtered,at least not directly. Besides,that movie clearly shows some humans becoming Gue'vesa(auxiliaries).
This sort of combative, ideological discussion is what happens when factions don't allow their diplomatic members to do their jobs. A bunch of non-commanding staff Astartes, culturally defensive seers, and non-Water Caste Tau couldn't cooperate themselves out of a cardboard box, let alone a war. I'll go find my diplomat, you go find yours. (Psh I'm not going to find a diplomat in 40k, I just wanted to say that)
I noted that. However, you don't show the same open approach to the Greater Good I've associated with other Water Caste discussions. Has the Tau become more aggressive?