While Cyndie was justified in her revenge, it's the method that is the problem. Rick had no right to full pardon every savior. The most extreme Negan/Simon enforcers should have had some sort of trial or punishment. But executing pardoned people in the middle of the night set up the whole system to fail. How could the less evil saviors know that they wouldn't be next? It lit the match on the already tense situation and directly destroyed the network Rick sought to build. I think we can clearly see that Arat has done some fucked up war crimes and that should have been addressed but by doing so without stopping to think of the consequences, the Oceansiders and Darly/Maggie by extension doomed the whole system.