I've noted before that the gold/red conflict was, according to my recollection, originally very cut and dried about golds good, reds bad, and that since then efforts have been made to lionize the reds a bit and vilify the golds so as to make the conflict more gray. I've also noted that I think this has only been half successful.
The basic point of contention regarding the golds is "they use chemical weapons". This is a serious charge, with these types of weapons being considered morally repugnant enough that virtually all modern states have agreed not to use them, though many make exceptions for retaliatory usage. The problem is that those same agreements ban the use of neurotoxin, which the red myr use even more casually than the golds because as the aggressors they use it on civilians. Brainwashing is not illegal, because there's no scientific backing to suggest it actually works on anything like the scale in fiction, but if it did exist it would certainly be in that same wheelhouse. Red myr venom addiction can be beaten, as we've seen, but still leaves deep psychological scars on the victor. And the reds don't even need to use it, because apparently they crush the golds in every battle despite their supply lines stretching halfway around the planet, making its use all the worse because of the lack of necessity.
I think a lot of this would have been solved by making the war an even match. Instead of Gildenmere being the last gold city on the planet and Kressia being a conquered territory, they ought to have been two cities on the border in a spot both sides agreed was the best neutral ground to host the aliens. Then you wouldn't have one side in a ridiculously bad bargaining position that makes the very idea of an equitable settlement laughable. You'd still have the need to do something about the gas warfare and find an antidote to red venom (preferably breed it out entirely from any reds that want to go offworld), but it would make it easier to sympathize with the reds and would make a peaceable agreement much more viable without requiring just outright booting the golds off their own planet.