It's a phrase used to mockingly refer to people who are very self-righteous in regards to issues of social justice. It's used by people with a sense of humor and also bigots, I guess. "Piece of shit" seems kind of harsh.

Calling someone who makes mild points about SJWs taking themselves too seriously and the absurdity of Japanese game shows "a total piece of shit" may be an overreaction.

"Proud" Republicans? Don't recall either broadcasting their politics.