From what I have read about them (I own the Codex since I wanted to start that army if I ever play 40k) that's not correct. Their philosophy has some similarities, but it seems that - in contrast to the Soviets who really didn't care a bit about their regular citizens - they really mean it. And the quality of life for regular dudes on their planets (even for non-Tau) seems to be orders of magnitude better than basically everywhere else.
Sure, they would easily pass as the bad guys in pretty much any other science fiction universe, but it seems that in comparison to the other factions in 40k they are probably as close to being called "the good guys" as it is possible in that universe.
...but then, the same would apply to the Soviet Union. Even regular 1940s Nazis would pass as the good guys in 40k.