Why is the both sides mindset becoming so prevalent?
Liberalism is used, cynically (imo), as a cudgel, to vote against real progressive politics. We can't have healthcare-for-all because we have to pick the side that isn't insane or else we get the insane group. And so on, and so on…
Look at how the Biden admin endorses genocide in Gaza. They completely ignore the masses of protesters calling for a ceasefire. How can they get away with this? "The other side is worse."
A truly responsive party would not stick its thumb in the eye of the people. It's not that both sides are equally awful. It's that both are awful and one uses the other to retain power.