Honestly it's because we all know (or somewhat know) that capital and capitalists are monsters and would put dissidents in gas chambers if able, the rest of the working classes also know this to a subconscious degree and will even express this via perceptions of how evil elites can be (whether conspiracy theory territory or not and just being credible claims). Once the glass does break though and gloves come off is when both sides understand that only one will come out of the conflict alive.