The Stormcloaks aren't all racist, though. Ralof? The fella at the beginning that you have the option of escaping with. My girlfriend went Stormcloak because I went Empire, and she told me he actually leaves Ulfric's forces. He agrees with the ideals of the Stormcloaks as a whole - freedom for Skyrim, and Nords, worship of Talos - but he hates Ulfric's bigotry and racism.
I'm quite sure there are more than a few young people in the Stormcloak Army that joined up to be freedom-fighters, or were drawn in by Ulfric's propaganda, that don't agree with him, either.
However, if the Stormcloaks win? Ulfric continues to be an asshat. And his Generals are in on the game with him. On the other hand, the Jarl of Widnhelm the Imperials replace him with actually deigns to do something for someone other than Nords - the Dunmer that are refugees in his city.
So, I think the Imperials have, on the whole - More "Good" personalities per capita. Having played through the Imperial questline twice, and seen the Stormcloak one played through once, it seems to be the case.
