I am convinced that the GOP’s current leadership will eventually fall, the extremists will be purged from their ranks, and they will become a relatively sane and rational party once again.

Such things don't happen by accident. The Republican party will start behaving responsibly when obstruction stops being their best move. Until then, their obstruction must be supported tactically by demonization.

Reagan and O'Neill met socially; Clinton and Gingrich did not. Gingrich figured out how to weaponize the virtual filibuster, how to make it look like the majority party wasn't getting anything done. Part of that process entailed creating enemies rather than opponents. There could be no excuse for "getting along" with such awful people.

The linchpin of this whole mess is that damn filibuster, in the form it now exists. So long as the majority needs sixty votes to stop debate, regardless of how many members of the minority show up to vote, obstruction will remain a winning strategy and demonization a necessary tactic. So, until the filibuster is put back its pre-1970 box, the Republican party will continue to spread hatred in service of obstruction.