I don't think it's normal people pushing the polarization, at least not in the root cause analysis. The political parties are playing the meta-political game of

I don't think it's normal people pushing the polarization, at least not in the root cause analysis. The political parties are playing the meta-political game of continuing to exist and the game theory there is to slice and dice the electorate along advantageous lines in every voting district/region. The more divisive an issue, the more predictable and reliable as a tool for staying in power. Political parties have no external goals; they are self-interested and use the people within them to achieve that goal by offering carrots (which result in fulfilling the external values of normal people) or sticks (which punish defection or opposing party members). Progressivism and conservativism are not opposed on a single axis. Political parties lay claim to and label particular issues which benefits both major U.S. parties in the long run by giving them each a grab bag of issues for a particular set of voters. This is why, for example, guns and wombs have opposite signs in the personal-freedom axis for both parties. As long as the shared belief exists that an issue "belongs" to "one side" it remains useful as a political tool but nearly worthless as a policy tool for normal people. Finally, it is not the extremes leading this charge. The core DNC and RNC execute this strategy because they are locked in a struggle for survival. The DNC and RNC have successfully used the threat of the least-aligned party to trap moderate and progressive voters within the party structures. Non-partisan primaries and ranked-choice/runoff voting are starting to show moderate success (AK and NH) at changing the game theory to favor politicians who compromise on multivariate issues versus enforcing party platforms.