Well, what did you expect? Deku had to stop the sadness somehow - am I right?

What point would have been with trying to engage Tomura in a discussion of his criticism of society? Of trying to make him see the changes? Of reassuring him that his friends are alive and there are people caring about addressing their complaints?

Did you expect him to use his genius quirk analysis skills to come up with a way to capture him alive?

Nah, you see, if you keep smashing at his soul until it breaks into pieces and the trauma and hatred will just go out. And then conveniently you can help his body be taken over again by paper-evil guy and then you can smash him to pieces.

That way, you don't have to worry about difficult questions like what you do with someone like him who has been groomed and targeted since before birth by the most powerful villain.

Never finding a complex problem that you can't just smash away with punches is the stuff greatest heroes are made of.