He didn't do anything though, the fight was already over. I dunno, maybe the anime did present it poorly, since I can't view it objectively, but it seems like you're focusing on details that aren't important, ignoring the bigger things because of it.
Well, maybe the anime is just different. Because in the anime he clearly saved all their lives and beat the final dude right before he killed them all. If that's not how it went down in the manga, fine, cool, the manga is probably better for it.
Edit: I really don't think that sweating the small stuff too much, in the anime this is the post climax climax of the fight, cutting away at the actual good part that seemed to be the climax with a directly opposite message.
Like I had said, it would have been a lot better if it had just cut off right before this.
I actually watched the anime more recently than the manga. In the anime, he came in and cleaned up a situation where the battle had already been lost and his organization would only lose face further if he didn't rebuke the guy. He wasn't part of the fight in any way, and it wasn't shown as a climax, but as an anti-climax, a fake-out. A last joke thrown in there. It's supposed to be a joke played on you, the watcher, but a good-natured one, not something that there's any reason to go get offended at, it's just silliness. Of course, it'll play into the story later, but that's for later.
Although perhaps ONE did mean to undercut the previous message a bit here, which makes sense. He was pretty heavy-handed with it, and it's in character for him to point out that no one viewpoint is necessarily 100% correct. I didn't initially think of it from that perspective because of what I know happens later, but it's possible that he did that to lay groudwork for refinement of the ideas, to come later.