The empire believes it has the right to sacrifice its citizens to pay its debts. It abandons anything not politically expedient to its goals and has no qualms about allowing foreign agents to abduct and torture its citizens. There were innumerable Redguard and Nord Imperial Legionaries who fought off the Aldmeri Dominion alongside their Imperial comrades in the Great War. How was their blood and sacrifice repaid? The empire cuts Hammerfell loose when they refuse to recognize the terms accepted by an emperor who only sought to appease the wolf at his door by giving their lands to that same enemy. In the land of Skyrim where worship of Talos, or Ysmir as he is known in the north is very important to its citizenry, is banned outright. His priests are now heretics, his shrines now targets for the Thalmor. What do you expect your complicity in the empire’s crimes to buy you? Silence never won rights. Freedom is not handed down from above; it’s forced by pressures from beneath.
Of course they have qualms about it, but they didn't feel like they had much of a choice, not when it was them who were in the Thalmor's crosshairs. The Nords didn't speak up like the Redguards (who, I may add, got what they wanted without actually fighting the Empire), not until the Thalmor realized they weren't doing enough and orchestrated the Markarth Incident.
Stormcloaks:
+ Don't give away information, like troop location, to the enemy.
+ Are not racist. The racism is only present amongst the population of Windhelm. And even there it's only directed at the Dunmer and Argonians.
+ Free Talos worship, Mundus lives another day.
+ Are capable of concentrating their forces if they ally with another nation, rather than forced to protect the Imperial City.
+ Plans to fight the Thalmor, rather than giving them time to recover.
- Ulfric
- Brutal
- Windhelm, the center of their government, is racist.
Empire:
+ The Imperial Legion
+ Titus Mede II
+ Tolerant soldiers
- Protects only itself, forcing others to die for them
- Allows Thalmor to kill Talos worshipers.
- Considers sheepish underground worship to be freedom.
- Allows Thalmor to see their troop locations.
- No longer considers Talos a god (try talking to Imperials who aren't connected to the Legion)
- Non-Legion population is racist.
Half of this is embellishment and speculation biased towards making the Legion look evil and making the Stormcloaks look heroic. Personally, I think either side could organize an effort to defeat the Thalmor, because both the Stormcloaks and the Imperials have good reason to loathe the Thalmor (the Imperials only agreed to the Concordat because it was their province the Thalmor were trashing, and at the time they didn't think they could defeat them. The Redguards proved otherwise but as they say, hindsight is 50/50). But I feel that a unified Cyrodiil and Skyrim defeating the Thalmor would have a better long-term political and economic outcome than defeating the Thalmor as embittered allies of circumstance.
The imperials ARE racist, in fact, arguably they are in some ways more racist than the stormcloaks.
For sure the stormcloaks are kind of backwoods, xenophobic, and stupidly, naively nationalistic....however the stormcloaks didn't conquer most of the known world and force it to adopt their customs and laws...if that's not truly, deeply racist and authoritarian i'm not sure what is.
As I recall, it was a Nordic warlord who conquered Tamriel.