Younger Dazai is an incredibly cynical person, obsessed with his own death. And being close to raw emotion and other people’s pain seemed, to him, like a way to deal with this. It’s mentioned several times that even other Mafia members fear him: he was the youngest executive ever, he’s a master torturer, him and Chuuya once annihilated an entire enemy organization in one night. Even Higuchi, who idolizes mister killing machine Akutagawa, calls his blood 'mafia black’.