The Stormcloaks are racist, unquestionably. Ulfric actively encourages his people to discriminate against the Dunmer, and treats the Argonians like farm animals (confining them to what's basically a cage). After Ulfric's death, if you visit Castle Dour, Tullius confesses to you that the Thalmor won't remain in power much longer. The Empire is planning an uprising and the Stormcloaks are ruining everything. There are undoubtedly some not-so-good members of the Empire, like the Captain at the beginning, and Idolaf Battle-Born, but they are the exception. Compare that to the number of scumbag Stormcloaks. Ulfric is a blind egotist; Galmar hates anyone who isn't a Nord, and Rolff...is just an a**hole. Ralof is pretty much the only decent Stormcloak in the game.