Yeah, I already thought Mori was in the "right" here lol though Gide is most definitely the one who responsible for Oda's death even if Mori brought them over.

I've been told Mimic caused a lot more destruction in the light novel than they did in the anime so finding a way to minimize the damage they were causing would have been the best idea. It's like lose a bunch of his own men or send off one who can pull off an one army stunt. Oda was the lowest in the hierarchy refused to do anything move up and likely to become turncoat given the chance. And he could match Gide in terms of ability. I'm fairly certain most of push back against his decision comes from people getting invested in Oda like Dazai did, which hey he's likable but it's very much a case of if it were a hundred random mooks we wouldn't care as much.

Literally wrote a fic involving this when I first got into the series lmbo

It's nothing personal. It wouldn't even be revenge at this point. Painful as it is, Dazai understands Mori's line of thought with his action back then. What was one person's life to a large portion of the mafia's protection? Other members wanting a relatively normal life would be able to function without fear of the police or government coming for them. Though he can't be sure whether or not Mori knew about the orphans or if that was the call of another member. It doesn't matter. Sacrifices are necessary, evil or not. That weight would always be on Mori.

One day he'll have to bear a similar burden.

"A leader is first a servant."