Why Care About Adultery?

Why care if one's spouse commits adultery?  Some might think people should care because adultery is a betrayal of marriage, but this is not always true in the way that they mean it.  If adultery is immoral, which would be a truth that transcends all situations, social conventions, feelings, and personal preferences, then yes, a married person should not have sex with anyone they are not married to.  To do so would be a betrayal of sorts if adultery is morally wrong.  However, this has nothing to do with the permissibility of polyamorous marriages, for it could not be adultery to have sex with multiple people of the opposite gender if one is married to all of them, and not all adultery is necessarily opposed by the other spouse.

Many who are against adultery would be disgusted by these logical truths.  They think that adultery being wrong would mean that there is no such thing as non-adulterously having sex with multiple partners in the same period of time or that all adultery is emotionally devastating to the other partner.  They also, more fundamentally, almost always only think adultery is immoral because of the subjective offense they derive from the idea of their partner having sex with someone else.  There is nothing weightier than this that motivates them or underpins their worldview here.  Once again, why care about adultery?

It would truly be shocking to them not only that logical necessities do not require what they think they do with this issue, but that not everyone even objects to adultery for personal reasons--which is invalid anyway.  Aside from my rationalistic Christianity and the possibility of contracting an STD, I do not fucking care if my wife (yes, I am now married) was to have consensual sex with other men. I am not an emotionalistic person to any extent, so that entire category of motivation is wholly alien to my experiences.  I myself am an example of how it is possible to not have traditional emotional reactions to such things.

I have no jealousy or possessiveness in my mind.  This is of course helpful when it comes to other things as well.  Even if adultery is evil, as the Bible teaches, things like opposite gender friendships, nudity shared between unmarried people, extramarital sexual attraction, and even acting on that attraction in specific ways is objectively nonsinful on the Christian worldview (Deuteronomy 4:2) and is logically irrelevant either way.  These things unlike adultery, are Biblical permissible and should never be opposed, but they are opposed for emotionalistic reasons just like adultery so often is.  Truly, there is no reason to care about adultery apart from objective morality, and that is if objective morality actually entails that adultery is wrong to begin with.

The only ultimate reason to morally care about adultery or any other deed is not because of personal dislike, which is meaningless, or because of some arbitrary emotional consequence of the action.  It is because it is immoral.  How many people really object to adultery on grounds that it contradicts Yahweh's nature (Deuteronomy 22:22) and that there is evidence that Yahweh is the real uncaused cause?  Specifically with all of these factors in mind and without making assumptions, almost no one does!  There is absolutely no reason to care about adultery or so many other things in the way many do other than the metaphysically irrelevant matter of emotion.