Because despite the stereotype, the Imperium considers the loss of a planet to be a grievous wound - there are a finite number of habitable planets in the Imperium, but an inifinite number of men that can be thrown at the enemy to reclaim them. If the cost is a billion soldiers to reclaim a Forge World, the Imperium will pay it gladly.
You also don't understand the nature of the Warp. Khorne Berzerkers, when they fight, are filled with nothing but rage and bloodlust. Their souls burn with it, and this empowers Khorne. Desire and sensation empower Slaanesh, decay and stagnation Nurgle, and shifting change empowers Tzeentch. This is proportionate to the souls being used.
The effort to corrupt the Tau for the meager gains it would give wouldn't be worth a God's time. They don't enter the Warp, don't have Psykers and don't have souls worth noticing.
Read the above in a Tachikoma voice.
This is easy to counter through the fluff – as the fluff says ‘there has never been any corrupted tau’. To counter the counter you can say ‘it’s a big universe’ or ‘these are the first’ or ‘it’s a tzeentch plan’ or almost anything ranging from the mildly plausible (if you ignore the fluff) to the raging bollocks.
But why should people object? You can paint your minis how you like and the rule of cool applies. The only thing people have an objection with using one list for another race, is not taking the rough with the smooth.
‘I think space wolves more accurately represent 40k World Eaters’ or ‘I use GK to be Thousand Sons’. This winds people up. So, other than rule of cool why would you do this? ‘Ah, for gameplay, I like my overcharged ion thingy and my support fire in overwatch – markerlights are the bomb. But I don’t want to play goody two-shoes tau commie fish people, I want the awesomeness of Chaos’.
Personally I think do what you like, don’t even bother with a mad backstory though ‘cos it aint fluffy in the slightest, you just crack on and stick some skulls on your manga suits.
I'M RATHER DEFINATELY SURE FEMALE SPACE MARINES DEFINERTLEY DON'T EXIST.
I like my armies to have a good back story that works with the overall fluff, even if I cross genra's. I end up putting a lot of research into my armies and their back stories. I've got lengthy backgrounds for my 'Halloween themed Eldar' army, my 'Star Wars Ork' army, Imperial 'Knights of the Round Table', or my 'Thousand Sons abusing captive Space Wolves' army.
Yes I misspell stuff, you'll live.
I remember when one of the Grey Knights/Daemonhunters books came out they did an article on why would Grey Knights fight each race. They had a Daemon Possessed Battlesuit Commander modeled up for the Tau. I took it to be that if a Tau leader is corrupted others will follow like lemmings. The whole Greater Good thing doesn't exactly encourage independent thought or initiative, and the Tau don't display the same selfish traits as humans. I suspect Tzeentch would like the challenge... plus the big T plays the long game. Who knows what strand of fate a corrupted Tau cadre may be used for in the future.
My Truescale Insanity
http://www.lounge.belloflostsouls.net/showthread.php?48704-Truescale-Space-Wolves
Typhus was always a psyker but was forced to hide his gifts because of Mortarion’s feelings about them. Still, Nurgle would be the easiest fit as though the Tau don’t relish in slaughter or excess; anyone can catch a plague. Especially a fleet from the 3rd expansion/outer fringes of “Tau space”.
It does sort of go against the Tau theme, at least until hell freezes over and GW advances the 40k universe's plotline, however I have a couple ideas how it might work.
I agree with the reasoning that there is no reason for chaos gods to directly take an interest in the Tau as a race however that doesn't mean there aren't other chaotic entities who might be desperate enough to manipulate a few dissidents. Maybe a cadre leader, with or without the knowledge of his firewarriors, rebel or go rogue, and end up allying with some chaos marine warband or make a pact with a stranded daemon they happen upon out of necessity for survival and this begins their slow descent to a more chaosy lifestyle? Unwitting pawns drawn in and influenced by an alliance of necessity.
And maybe the reason why no tau have ever been corrupted is because that what the etherials want you to think! I mean, there's probably been a few renegades, some of which survived the inevitable purge, and without the numbers, resources and cunning of the Farsight enclaves, it would only be a matter of time before one is subjected to this specific kind of bad influence. Galaxy is full of em.
The Eldar have huge signatures in the warp. They a beacons that can be found very easily. Humans have a very small signature. Barely noticeable but because of how many humans exist, entire populations can be easily seen in the warp. The Tau do not and I repeat do not have any signature in the warp. The Tau literally have zero connection to the warp. The chaos gods can not corrupt them because the can communicate with them or contact them ordo anything. They are like anti-force creatures from star wars. Now I think that Tau machines can be possessed by chaos but possession of a weapon or a machine requires great rituals and sacrifice. I don't think the Tau would do that to one of their machines. But the possibility of corrupted Tau battlesuits is possible in the fluff.
The problem with this scenario is that it is too much investment for next to no gain for the big gods. It is not affordable for the lesser ones.
You guys keep thinking that Chaos need an army. But they do not need an army. They already have an unlimited amount of warriors.
What they do need is fuel. Fuel to keep daemons in reality, fuel to feed on and fuel to make posessed work. This fuel is the spark of energy which is called soul. Tau do not have them or it is so insignificant that they enjoy near immunity from attacks of warp predators.
The Tau are basically a better alien version of the emperors vision. Atheistic and next to soulless. No food for you chaos gods.
If Tau would rule the galaxy Chaos would start to wither and die as there is nothing to feed on. They have to be eradicated as there is no failsafe to keep them in line (pacts).
Just because they can scheme, rage, rot, be sadistic or can be manipulated this does not mean they are of any use to the gods as they do not provide anything to them they could possibly need. They are a danger to them... and the Ethereals are probably gene engineered by the Eldar *cough*
Indeed, Charon is right. It'd be like invading a heavily fortified planet just to grab a barrel of oil. The Dark Gods are vast and intelligent, and they aim for the biggest immediate reward for their efforts. After all, every moment spent glancing at reality is a moment away from the Great Game.
Read the above in a Tachikoma voice.