Why are you assuming the surviving partners necessarily has worse judgment than the person you originally went into business with? It sounds like you're arguing from a default position of not trusting other people and needing to defend your enterprise against outsiders, which is likely to be a limiting factor on business growth sooner or alter. You might be better off with a professional corporate structure, like a legal partnership.

Facebook and Google both have founders who have more voting rights than their ownership stake would usually allow.

But in the case of the Reddit thread, it seems like her spouses business is more like a partnership. Even with a legal partnership, she is a joint owner in the partnership by default unless some other arrangement is made.

Just to emphasize, if the purpose of the postnup is to keep her from benefiting financially from "his" success while they are married, I find that completely distasteful. But if the purpose is to protect the integrity of the partnership, I don't see a problem with that.

I don't think my wife would want to have any part of the day to day decision making of a computer related company I started and let's assume I wouldn't ask her for a postnup and ask her to sign something on the event of my death that would allow her to be bought out at a fair value or allow her to keep her equity but it be non voting.