I think there's been a miscommunication. I don't have any such mod and know of no way for them to have sex outside of sharing a bed, so I'm asking why the game prevents them from sharing a bed but also gives a mood debuff if they have sex when it's impossible for the to have sex without sharing a bed.

You're not on !rimworldporn@rimworld.gallery , you're safe

Be glad it wasn't yet another war crime!

Some of my colonists were engaged. One had free and accepted physical love, but the other had spouse only (strict). The game would not let me assign them to the same bed. If there is no way for them to have sex outside of sharing a double bed, then when will the mood debuff ever be applied?

Caveats and assumptions:

1. I did not confirm that the wiki is accurate with the in game values for the various possible values for the precept.
2. I only experimentally tried with spouse only (strict). It's possible the wiki is incorrect and the other forms of spouse only don't forbid bed sharing. I'm pretty sure the button to assign the abstinent pawn was simply gone. As soon as they were lovers I wanted them together to save a room. I think I would've clicked it even if there was a penalty.
3. I only experimentally tried with the free and accepted precept pawn having the bed first. It's possible that maybe having the free love pawn move into the abstinent pawn's bed is allowed.

I get your point, sometimes you can tell them to do things they don't wanna do and just take the mood debuff. But that's entirely why I'm asking. Because I couldn't even move them into the same bed at all. So it's odd that there exists a mood debuff when it's literally impossible for them to do the deed.

Point 3 seems to be the next thing to investigate but they're already married now. Most of my pawns have free and accepted physical love, but I can try later tonight and see if a free and accepted pawn can move into an abstinent bed (even if an abstinent pawn can not move into another non-spouse's bed).