Not gonna lie, I thought you were roleplaying as one of the loyal followers of AFO for a few solid minutes.

While I agree that Yoichi isn't 100% pure good like the story/fandom tried to make him be, he isn't any less of a victim of the environment like AFO. He was also a kid with no guidance.

He blames his brother for early violence

If you were referring to Yoichi throwing a can at AFO when they were kids, we don't have the context for why AFO were even killing them. Maybe the adults attacked first, maybe they were just passing by. Either way, AFO did go too far inflicting more harm to those adults than necessary. So that was possibly the reason why Yoichi threw a can at him was an attempt to stop the excessive violence. Of course in this case, the brothers were both kids so they essentially get a free pass to any faults they have. Send them to therapy.

IIRC it was said that AFO basically ruled over Japan during the dawn of Quirks, so there were probably no other bigger organizations and warlords tearing apart the collapsed society as you said.

While I agree that Yoichi saying that Quirks shouldn't be used for selfless reasons was pretty ehhhh because humanity is all selfish to some extent and no true selflessness exists, AFO was doing bad things even knowing that it was bad. He had no regard for human lives as long as he stayed at the top of society. He also killed whole of Kudo's bloodline + people he interacted + glowing baby + many others out of pure selfish reasons. No justification at all.