A counterfactual controversy
Bob: Me and Mary had a baby!
Alice: Huh, wow, interesting - aren’t you still in a relationship with her?
Bob: yeah… I know it’s weird, but I’ve just never understood what’s so bad about having children with your partner
Alice: you’re a funny one Bob. Does the huge conflict of interest not faze you?
Bob: how are the interests in conflict? I would have said they are aligned..
Alice: That’s what conflicts of interest are like—you’re Steve’s brother and also the person in charge of employing him: how convenient. But you are meant to have an interest in something else! You might prioritize Mary too highly among other potential partners because you have children with her. You might view her childrearing through rosy lenses because you love her—
Bob: I do! She’s amazing, I see her holding Isabel and it’s like everything is perfect in the—
Alice: See! That is not rational childrearing speaking. You won’t give her the proper feedback. The children will be neglected.
Bob: but—
And that’s not even the biggest problem. What if something goes wrong in the relationship? Do you want it to wreck the coparenting?
Bob: I agree that’s a risk, but it’s so worth it! And I think it’s making the relationship stronger. And the relationship makes our coparenting stronger. So they are both less likely to fall apart than they would be..
Alice: —and these are all just reasons it’s pragmatically bad, and bad for the children and your other partners. If you want to know why it’s so ick, it’s because of the messed up power relations. Now that you have children together, you can push her into doing anything by threatening to abuse the children.
Bob: But we love each other! And I love Isabel! It’s true I could put her in a terrible situation in some alternate universe where I’m a remorseless asshole, but wouldn’t it be better for my peers to watch out for the possibility I’m a remorseless asshole (which would probably have other signs) than to watch out for me ever being in a situation where someone needs to trust me?
Alice: That’s what a sociopath would say
Bob: Alice, we’ve been friends for fifteen years… When you came over for my birthday the other day and I was cutting the cake, did you also judge me for holding the knife, since I was in a position of power over those I could have murdered with it?
Alice: Yes Bob, you’re great at philosophy, but I’m just trying to help you out here. It has a bad vibe, everyone feels really ick around it, probably for good reasons. I’m just trying to help you see why.
Bob: But I love Mary so much, I just want to spend every day with her, and do everything with her. Our life is a dream. It would have been such a huge hit to have a child with someone else, or to break up so that we could have a child together.
Alice: There are a lot of other people! You can find someone good to coparent with. And in a way that’s fair and gives other people a chance. Because you are also making the community unwelcoming: people with great parenting skills are out looking really hard for someone to coparent with—and then you shaft them for someone totally unqualified who you have some conflict of interest with—who you are dating for Pete’s sake—
Bob: —we’re actually married
Alice: [rolls eyes] Do you have no shame?
Bob: Um, and um, we live together…
Photo by Ilya Pavlov on Unsplash

I don't know what this is a counterfactual to. The normal situation where having kids with someone you're NOT in a relationship with is slightly controversial?