At first killing mori had given Dazai a bad reputation.
However people like Chuuya, Hirotsu, Akutagawa, and many others in the mafia found out the reason why Dazai killed him and the word soon spread causing many to support him.
People like Yosano were extremely happy at the fact that he had killed Mori that they told the other people in the agency to not go on full on war unless it was neccassary.
The death of mori bought Yokohama peace. the guild did not dare fight them. They were weary when they saw Dazai's reputation of 138 murders 312 cases of exsortion and 625 cause of fraud but then decided not to attack after finding out that, that wasn't even half of his crimes.
Fyodor wasn't much of a trouble since he and dazai had the same mind so Dazai could deal with him for the time being.
Chuuya was by Dazai's side most of the time. Chuuya understood why but he had never expected dazai to be this opposed to let him die and Dazai was becoming more overprotective by the day as he heard news about more and more of Fyodor's victims and all of which were in the port mafia.
He knew it was only a matter of time before the black lizard, the executives, and Akutagawa would get targeted. Of course if that happened chuuya would die.
So he had only one option.
He'd die fighting Fyodor alone, or die fighting Fyodor with chuuya. Which is basically double suicide. And as much as he loved the ginger dying with him was the worst scenario imaginable.