If we don't have meaningful language to describe political principles and how and why policy goals are pursued, this is what can happen: We dismiss our opponents as evil. As stupid. We assume that they only reason that they could disagree with us is that they are openly hostile toward the things that we 'know' are good, or that they are simply ignorant of the 'right' information that will help the scales fall from their eyes. We set out to 'fix' people rather than inform them and ourselves.
I don't think this is exclusive to modern American liberals, even if they're the ones who may have best transferred the attitude into popular culture. I have met and know many conservatives and real liberals who are just as guilty. There is a powerful seductiveness to the idea of being so right that ignorance and evil are the only things that could make someone disagree with you.
This environment is corrosive to the democratic debate that forms the backbone of a functioning liberal democracy. It is corrosive to the stable set of rules for governance that help encourage positive, rather than negative or ungrounded, change. It replaces them with disdain and encourages unbound populism. And it makes people mean.
No one is perfect when it comes to how they engage with their interlocutors, but try to recognize when you've failed to see the merit behind an opposing point of view. Assume good intentions, and try to rein it in your reflexive indignation . Push back against vacuous language. Treat each other like humans. And I think things can get better.