As a child of divorce, I totally get on why he would want his parents together. Plus, Ken was barely in college when his parents split up. He seems like a very emotional person compared to his sister. He values peace over chaos.
Very fair.
On the flipside--this isn't "peace" so much as a veneer of normalcy that is mostly just Goto subjugated under Akemi's antics.
There's nothing saying Akemi will suddenly stop her historic behavior because she's now carrying Goto's child. Ken isn't wrong for hoping, but he already wants his sister Moe gone (again, understandably). But my read is Ken just wants his father and mother under one roof; not his
family.
And it comes across as selfish, because even as he knows at least some of what all is going on, he's seeking his own satisfaction and wants over the wants and feelings of any of the others.
And it's a meta call, but it's not lilely to last, much less last long. He doesn't know that, of course, but my comment was based on the narrative direction and his character within said narrative.
I can sympathize with him as a person, but he is simply desiring 'negative peace', over anything that could actually be called a stable home life.