The Civil War was imperialism but it was good imperialism. Fascist breakaways are a bit different: the Union taking over the South was infringing on their self-governance, but that's a good thing, Confederates were pure evil. It's like after WWII and Axis powers became occupied, could you technically call that colonialism? Maybe, but they needed to be.

If Taiwan was blatantly fascistic, genocidal, had slavery, etc. I would support China colonizing them... but they aren't. They're neoliberal (much like China), which is lame, but they're not a Nazi state. Remind me, who was the first in Asia to legalize gay marriage?

Your comparison is bad faith.