Color me unsurprised. Read Thomas Sowell's "A Conflict of Visions." People on the Left -- people of what Sowell calls "the unconstrained vision," often CANNOT disagree respectfully. You get some of that from their ideological opponents -- people of "the constrained vision" -- but not nearly as much. It's far, far more common for leftists to be unable to disagree with you and remain civil to you. They regard you not just as someone who disagrees about how best to achieve the desired goal of a better, more civil society, but as a bad person, a moral defective, and therefore someone who is to be spit upon.