Sarcasm has to be clever to be effective.
The argument is about whether or not Morrison's phenotypical appearance-- which at one point was supposed to be THE standard appearance for Storm Troopers-- would have led fans to think that any other Clone Troopers could be black at all, much less look specifically like John Boyega.
In his appearance as Jango Fett, Temuera Morrison does not display an appearance that signals his POC status. He could be Italian, Spanish, or even Black Irish-- the last being closest to the mark, since he's supposed to have some Irish ancestry.
Ultraliberals don't want to just control people's minds; they want them all to be mind-readers.