Why does anyone care? Well perhaps because it affects society at large.
It will spread more STD's, which we will all have to pay for, it will create more unwanted children or abortions, which we will all wind up paying for, it will cause more broken relationships, which again filters down to harming children, and we have to splain and try to convince our children that this is wrong and that they should not embrace it, even though more and more in society seems to be doing so.
If the couples have unprotected sex, you might have a point. But I can say from personal knowledge, the "kink community" is more adamant about using condoms than any group I have talked to.
Condoms fail, and condoms don't prevent relationships from being destroyed either.
Maybe they can wrap giant condoms around their children during the divorce.
Cheating destroys more relationships than open relationships do. What the children know hasn't stopped men & women from lying and cheating throughout history.
I see, so the options are cheating vs. open relationships?
How about not doing either? That will save even more relationships.
It reminds me of the condemnation the Catholic church received for speaking against contraception. All the news was about spreading STD's thanks to the Catholic church. But then I did something inexplicable. I began to think for myself and realized the absurdity with that line of reasoning. If you are going to violate the Catholic church doctrine by having sex outside of marriage then why listen to them about not using contraception. That's what they call insane.
By all means, if you are going to do it anyway, then be open about it, much like you should be honest if you want to murder someone.
By all means, if you are going to do these things anyway, they you are on your own and many will suffer as a result even if you take precautions