They want to escape an obsessive, cultist, military dictatorship. What exactly is selfish about that? What is selfish about Cid's reasons for defecting?

Garlemald is invading, and doing nothing good while doing so. Cid has very clear (and, frankly, very sympathetic) reason for wanting to ditch that noise. Garlemald uses science and tech at the expense of its own citizens! He's out. He's done. That's good motivation! We don't know Lucia's, but...dude, look. At some point, you're going to need to admit that these guys are closer to the Nazis (or Imperial Japan, or whatever) than they are to Rome. THEY ARE THE BAD GUYS. They enslave and conquer for no purpose other than that single, selfish end. If a former Nazi defected, and it led to the death of some German soldiers, that's war and perfectly understandable. Why can't you apply that logic here? You talk about pragmatic interpretation, yet you're blind to how the story presents this nation.