Part of the drama in The Expanse revolves around people making shitty foolish choices because they overestimate their position. The OPA and Earth getting into a military exchange, and the fallout that ensues, isn't a bad subplot on its face. Each side assumes the other will blink and... they don't.
The conflicts and the ensuing mass migration are a big part of the story. Cut that stuff out and there's not much of a show.
Also, I think "The OPA is socialist" is a bit of a stretch. They're anti-Earth liberationists, but none of them seem shy about doing their own brand of localized capitalism. If any place is socialist, it's Mars.