Every single Villain in the series was a justified good guy because SS have been the villains from the start.
The zero squad really reports to the SS noble families.
The spirit king is a corpse because the noble families attacked him to gain his power before dismembering him and he is still somewhat aware/conscious despite being dead.
Ywach was fighting because he wanted to save his dad from what he considered a fate worse than death.
SS was going to dismember Ichigo into the next spirit king but ywach decided to save him from that fate at the end.
Ginjo(Former substitute shinigami) did nothing wrong because SS randomly tried to assassinate him out of nowhere and he was trying to figure out what the hell was going on and get to the ones he thought were responsible for the attempt. The SS involvement in the entire Fullbringer arc was just to trick ichigo into bringing out his heroic side again so that they can use him.
Aizen knew about what the noble families did(original sin) and was trying to do a rebellion.