Two thoughts:

1) "Political correctness" has always meant "excessive language policing from the left" rather than anything more concrete—it was a pejorative term even before it was introduced to the general public in 1990 on the pages of the New York Times—so it's no surprise that it has a bad reputation.

2) It's kind of ironic to use a research paper by a group called More In Common, who seek to counteract polarisation, to slam a particular political group.