I see your point. It's possible I'm conflating a bit here, but I see certain groups hold on to some ideas like "sacred cows". E.g. many feminists would say "If we can make all outside factors equal, females will participate in STEM careers as frequently as males". And if one were to challenge that idea, one might be accused of being politically incorrect or insensitive or something similar.
I think that cries of "that's politically incorrect!" come more frequently from the extreme left, but I don't think that's always the case. My example of the trickle down idea seems to me to be a "sacred cow" for the right, but perhaps to question the idea would not be met with cries of "politically incorrect".
So maybe it's more accurate to say that sometimes when sacred cows are challenged, the response might be "that's politically incorrect!".