This viewpoint is the culmination of years of hacking the Overton window. In any two-party environment where only _one_ party regularly _does_ proliferate bigotry and violent attitudes, any reasonable/neutral observer will appear to be a partisan for the opposition by default.
To assume this wouldn't be the case wrongly assumes that ideas should naturally fall along a Normal distribution, with the most morally-correct views centered precisely at x=0 (bipartisan) along the left/right axis.