I call it Performative Emotional Synchronization. If the lefty considers a thing good/bad, then they expect people to match if not exceed their level of "joy" or "hatred" when the topic is discussed. Outright refusal, a more measured reaction or even a moment of hesitation mark other parties as outsiders or enemies.

Does not matter if they actually believe or understand what is being discussed, or if they had a completely different take yesterday, or if you have known them for years and discussed the topic previously, only "get on my level of virtue signaling or else".