So, even ignoring that high horse you're on: in your not so humble opinion, are all registrants on ALM guilty of marital infidelity? That's assuming guilt by association, and flies directly in the face of your own constitution.
The point still somewhat stands that if you and your partner had open-marriage or something, your friends and family might find out.
In which case, just pretend you were cheating on her and carry on (if price of outing you as a non-monogamous couple is too high).
Marital infidelity is illegal in 21 states in the US, and many other countries as well. For many individuals this is not just an ethical concern, but a legal one as well.
So yes. It's illegal. In some states. Has largely been determined to be unconstitutional, your handwaving of "these people broke the law, they get no sympathy" notwithstanding.
There have been less that a dozen misdemeanor prosecutions in the last half century in those 21 states combined.
So yes, in those states, it's illegal. Just as in many cases, so was homosexuality, and anal sex.
I'm disappointed HN has a blanket ban against Gawker links, as the Geithner story there from a few weeks ago has some very important lessons for this story.
In most marriage ceremonies, the couple stands in public (at least in front of the people who care) and makes a series of vows. If that's not a vocal stand, I don't know what is.
And marital infidelity is unethical even if it isn't illegal. It's pretty FUCKING SHITTY to lie to your SO, sometimes for YEARS, exposing them to disease and finally ridicule and humiliation, and their own right to make informed choices about their precious time and trust they invest in a person. It is selfish and rotten and deprives the other person of agency.
edit: on this account I have complained about Internet mob culture multiple times. I was hoping that people would recognize that I was pointing out the hypocrisy of people on this who don't care when it happens to people who do things they personally hate, but I was way too subtle. Resharing this data is a shitty thing to do, but it will happen again and who decides at that point that it's still shitty entirely depends on who is being exposed.