My argument for this is that in a longterm relationship, not everything can be voluntary. By voluntary I mean you'd rather do that thing than anything else at that time.

This point should be obvious, but relationships and marriage are a contract. Not all of the stipulations are written down, but the whole concept of a marriage is a contract. If you cheat, stop doing anything, etc you're breaking the contract. A relationship is different from FWB because there's actual responsibilities of some kind.

Now with covert contracts: I think it's reasonable to expect done kind of reciprocity in a relationship. For example, if I'm not a deadbeat my spouse should do the bare minimum. This isn't bad logic - because marriage is a contract, so if you're doing your job they should do their job. It's also reasonable to do your job with the hope that they'll do theirs. This is also normal- you have your friends back and hope they'll have yours.

Sometimes you might have a dumb idea as a covert contract - "If I go see my in-laws my wife will act like a pornstar." But that's just dumb. It's reasonable to think "if I'm a good husband my wife will try to be a good wife." If she isn't, that's not because your logic was bad, it's because your wife is bad. Lol