The Imperials are nowhere near as racist as the Stormcloaks. Legate Rikke, one of the highest ranking soldiers in Skyrim, is a Nord, and every race but the Khajit is present in Solitude. As I recall, I have seen Dunmer and Altmer, as well as various humans in charge of Imperial camps. The Stormcloaks are all about 'Skyrim for the Nords', and actively oppress the other races (Dunmer and Argonians most obviously) for nothing other than their race. The Imperials can be equally as cruel, but for the most part they discriminate people for their actions and doctrine rather than for their heritage. The Argonians and Dunmer (and Forsworn) did nothing to deserve their persecution by the Stormcloaks: the Dunmer were simply fleeing the destruction of their homeland, and were distrusted for nothing more than their arrival at a tense time; and the Argonians suffer for much the same reason. The Stormcloaks follow the naive mindset of inherent ownership of land due to little more than happenstance of birth, and are terrified of change and are hypocritical to the extreme - starting the civil war to attempt to liberate 'religious freedom' and yet persecuting other races due to fears of their culture 'muddying' the Nordic ideal.