Jayce is explaining because he does want it clear that he did the wrong thing. He was definitely pushed past the point of reason by Jinx's constant violence and her ability to use his technology to kill people. The hopelessness of losing Viktor combined with righteous anger and frustration at a system he'd believed in that turned out to be corrupt, it made a very bad stew. Mel told him he had to create weapons so they could defend themselves against it, and at the time, he would've never thought he could brandish a weapon let alone do anything like that.

"I've heard that from others too. I guess irrational emotions make fools out of a lot of us." Jayce is so pushed forward by emotions. He is the smartest person in his world, along with Viktor, but Viktor can be reasonable, and Jayce lets his heart guide him more than his head. And he learned a lesson about that.

"I think the lingering issue I'm dealing with is facing an ugly part of myself. You have to understand, I'd never been in a fight in my life really, I'd never responded with violence to anything." In that they may be different, but that's where a lot of the struggle stems from. To be a peaceful person at the core. A scientist who only builds, not destroys. "It turns out I have an anger problem that I wasn't aware of."

Kell saw his passionate plea to the Council all those years ago, and his restrained anger toward his mentor, but neither spoke of actual violence. Emotional, yes, but clear-headed, genuine, sincere. This was something else entirely. "I'm worried about how easy it was, if I'd do it again." Jayce is only worried because he does think that he will.