Why is adultery a crime in the military?

Adultery and Article 134 of the UCMJ: Elements
(1) That the accused wrongfully had sexual intercourse with a certain person;

(2) That, at the time, the accused or the other person was married to someone else; and

(3) That, under the circumstances, the conduct of the accused was to the prejudice of good order and discipline in the armed forces or was of a nature to bring discredit upon the armed forces.
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As long as they aren’t married and the soldier isn’t married I don’t see any problem with it. It’s only a crime when one of the two is married, which I do have a problem with. It brings discredit upon the armed forces which is why Article 134 is there in the first place. If the soldier wants to sleep around he either needs to get divorced or work something out with his wife (some people are into that).

Military life is hard enough without adding in this sort of conduct.

My opinion is that it comprises the mission... whatever it is. Just half a century ago, it was scandalous for those relations to happen anywhere outside of marriage. The interpersonal conflicts it attracts can affect a soldier’s ability to perform. It could be used against the soldier and compromise security. It had been illegal in all 50 states. In some states there is still a law against “Alienation of Affection” (NC is one) which is still effectively used by spouses to get redress of their grievance against the party that “took” their spouse. Single or married, a soldier can find themselves sued for that... interfering with their readiness.

The very simple answer: because it was not deemed to be dropped as a crime. No matter how you, or your buddies, feel about Adultery, it is a crime as defined by the UCMJ.

Now, to get into it a little deeper. It is a crime of betrayal of trust. If a person is willing to betray trust in this type of relationship, then what is to stop them from betraying trust with your brothers in arms?

Because 1. It is against the law in most all states if they chose to prosecute. 2. It is against the good discipline in the Army. 3. The regulations say so. 4. Leaders have better things to do than get the repercussions of you love life.

Why? Because it can cause a lot of personnel issues within a unit when it happens within the Service Community and it can cause issues even if one of those participating are not involved with the Military. Other than the with the hypothetical soldier, I mean. It's nasty enough in the civilian world just dealing with the aftermath of divorce, property and custody without having to consider the effects on the soldiers performance and how that effects others around them.
I've seen it end the career of more than one Senior NCO and Officer.
Now it doesn't stop it and it's seldom prosecuted unless in conjunction with other offenses. So if you are having an affair with some Civilian that isn't associated with the Army and you don't have any issues with her or her Husband/Significant other, even if common knowledge, chances are you wouldn't be prosecuted. Now if her husband shows up on base and unloads on the Commander, things might not be that smooth for you after that.

Many things in the UCMJ that date back a long way... try "Abuse of a Public Animal"... for example! Adultery as a crime probably dates to our shared Judeo-Christian heritage, and, might have been connected to the notion of maintaining good military order and discipline. As the military was once much, much more isolated from the general public - especially say the Army, out alone on dusty bases far from civilization. So, any affair under those conditions was probably with the significant other of another service-member... which of course is pretty destructive when it comes out... and it always comes out!

SFC Thomas-I think the logical rationale is that it shows lack of integrity. The more pragmatic answer may lie in the overall impact to readiness and security a divorce/marital issues can create.

On a personal note - you can ask my ex-wife - she cheated with 3 military members - I had charges brought on all 3 - if it was not for the charges all 3 would be eating their food from a tube for the rest of their lives....The UCMJ saved them a lot of pain.....sorry to but had to be honest

If your personal life is out of order, it causes disorder in your professional life. If you're off your game, you risk not only your life, but the lives of others.