I think everyone there wondered that, actually. If he wanted anyone to trust him, he certainly didn't do himself any favors... but I assume he would have been able to predict that.

[ He can't stand Dazai, but he knows he isn't stupid. ]

He said he wanted to show you that there was no de facto leader among our group.

[ Though most of them are obviously shitty villains who wouldn't want to follow anyone anyway, so that doesn't exactly seem like a role anyone would have assumed to have existed. ]