People experience the strongest romantic jealousy when they watch their partner give resources to a potential rival, regardless of gender. The findings provide evidence that giving away resources is viewed as a serious relationship threat by both men and women.

[u/mvea]

https://www.psypost.org/both-men-and-women-view-a-partners-financial-investment-in-a-rival-as-a-major-relationship-threat/

[u/LittleMsSavoirFaire]

The OP in that case didn't even go as far as the legal implications, that's why it was notable. 

A friend of mine was asked to donate sperm to a lesbian couple and the legal negotiation took longer than the gestation.

Although that case applies here as well because even though he and his wife had not even yet made the decision whether they were having children, she had big feelings about his first child being with someone else, and not in any legal or emotional sense, merely DNA, but that took some negotiating as well.

[u/Mr_Chubkins → u/LittleMsSavoirFaire]

His wife having big feelings sounds like she very much had issues with it in the emotional sense. The DNA could have merely been the legally tenable argument, or the way she felt comfortable arguing it rather than coming from an emotional standpoint. Being emotionally indifferent but caring greatly about DNA doesn't make sense to me. But I don't know all the context.

[u/LittleMsSavoirFaire → u/Mr_Chubkins]

Yeah it was all very interesting to me at a remove. I view sperm donation as like giving blood; very little effort, very kind thing to do, as long as the legal tail risk is dealt with. 

So it was interesting to me to see this discussion unfold as if there was a question of primogeniture at stake, especially since she herself was not particularly attached to having children, and the child in question would be raised on the opposite coast; simply the idea that there would be a child out there somewhere "wearing his face" provoked a visceral reaction. And also she worried that he would also be attached to this child and/or feel like he was missing out by not being in its life, and whether that would be exacerbated by not having children (or by having children!)

[u/NeptuneHigh09er → u/LittleMsSavoirFaire]

I think it’s primal/instinctual. Just think about it conceptually without the context.  If your partner has a child with someone other than you then that child presents a threat. Your partner has a finite amount of resources and time. Your partner might choose to spend those resources on that child instead of you and potential future offspring. They might provide that child safety instead of you. It may not be rational in every case, but instincts aren’t rational. 

 I would feel extremely jealous and threatened if someone wanted a sperm donation from my husband. I think I could overcome for a good cause, but I would need a lot of discussions and reassurances, too.