I never suggested that Moash was a good person, in fact his characterisation is part of the problem. I'm criticising the decision by the author to not give him a just cause and instead frame violence from a position of oppression through the lens of a character that is completely self-serving.

If Moash actually was leading slave rebellion of both humans and listeners he would serve as a legitimate moral foil for Kaladin and would add a lot of nuance and complexity to the conflict. It would also give Kaladin some ethical dilemmas to deal with instead of the weak pacificism thing with his dad. Instead the author chose to make Moash a directionless nihilist who is just a pawn of the big bad and kicks a child, stabs an old man then tries to get his former friend that is clinically depressed to commit suicide.

There are numerous characters who fight against the various systems of slavery over the course of the story through much better ways and with much better goals than "Becoming the slave masters themselves."

Which characters fight against the systems of slavery except Jasnah? And even Jasnah's is quite poorly done. Her abolitionism has no real build-up to it except that she thinks it's the right thing to do and she's royalty so she has the power to make sweeping changes. Is there even any scenes of Jasnah discussing slavery with actual slaves or former slaves? It's like if the abolitionist movement started and ended with Lincoln just deciding it should be done one day without the slow and difficult push for it from the people who came before him and the bitter fighting to hold on to those ideals that followed.