...for spouses to keep their respective financial affairs as separate as possible.
The same logic can be extended to other affairs as well, but that is neither here nor there.
No argument here, because it would devolve into what marriage means and where you and I come from. But if people want to keep things from their spouse, they have no business being married. (yeah, sure, keep your cheerleader-nun sex fantasies to yourself, but to keep your finances to yourself, no, wrong.)[ Parent ]
Form an LLC or LP or somesuch.
My original dictum is meant to be a rule of thumb and; it should be broken only with careful consideration. While the incorporation thing may seem extreme, by placing a barrier would tend to ensure some level of careful consideration.
Further, depending on how the incorporated entity is structured, one owner need not bear any liability for the other's actions.