Both Nords and Bretons are sentient and sapient on the same basic level, so it's not an accurate comparison. I think you could compare a Nord being a racist to a Breton to a human being racist to a sentient alien*, which is another form of Fantastic Racism in fiction. In many sci-fi, however, enmity towards sentient aliens is considered to be bad, unless these aliens have clearly hostile or warlike intentions. Fiction derives its impact from both parallels and differences from the real world, after all. Not that Skyrim is that xenophobic, anyway. I agree that Stormcloak bigotry is quite minor and vague, in order to make them more bigoted you have to resort to mods or headcanon. *albeit to an alien with whom humans can have kids, and who basically look like humans, anyway. Now that I mention it, the large difference between human and elf lifespans in TES could be a reason for more than superficial difference between races, but it's very much downplayed in TES writing.