I consider Tzeentch the one Chaos God who isn't doomed to be a villain of the universe, the Chaos God with the greatest capacity for genuine good as well as evil. Nurgle at least claims to be the good one, but that's only from a twisted philosophy that torturing people with disease until they join you is somehow the most generous thing in the universe. And harmful ideologies are way worse than simple amorality

Personal plot twist that Tzeentch is actually a good guy, but if you live in the Warp people tend to lump you together with the bad guys who also live in the Warp.