I can't speak for others but when it comes to this now timeless discussion, I always have to remind folks that I'm fighting to drive the Thalmor out of Skyrim, to beat back their tyranny and weaken their influence - and guess what? I'm in the bloody Legion! At the end of the day, we can only speculate on the precise nature of the Dominion's resources and war-preparedness at present. However, to me, a united Empire is the best hope for finally washing our hands of them in the future. If we presume that they are in fact weakened to a considerable extent post-Great War, it makes sense that they're utilizing a conquer-by-proxy method, and utilizing it effectively. I see the events in Hammerfell as a very clear example of the Dominion's 'divide and conquer' strategy and given that they're using it again in Skyrim, I want to be able to call it out for what it is and kick it right back to them. As I've said in other threads, I don't begrudge the Redguards their strength and determination to keep the Dominion in a stalemate, but I also honestly can't discount it as a calculated result on the part of the Dominion.
I have immense respect for Legionnaire Nords like Rikke and Hadvar who count themselves 'true sons and daughters of Skyrim' every bit as much as their brethren on the other side. I truly believe that most of us who fight on the Empire side greatly despise the Thalmor and the machinations of the Dominion.