For example, a person fights (or claims to fight) against racism in the manner of believing a group/ethnicity/etc. (in a culture where this group is often disliked) to be morally superior, and if a member of this group commits something bad, this person refuses to believe it, and calls everyone a racist who dare to say anything but praise about people from that group. Or, this person being an advocate against prejudice, and fighting for "equality", but in fact vilifying and being prejudicial against everyone who does not share his/her exact political beliefs.
Is there an English word or short phrase, to express the above attitude in a much shorter way than that whole paragraph?
I thing demagogue is not the word, because it means that a person claims to have other beliefs as he/she really has, for gaining some advantage.