Exactly what are you talking about here? Are you asking about the specific case I was referring to? Or are you asking me to address all such relationships. And to what extent are you speaking of when you say "harm"? Are you referring to the people involved? Or are you attempting to include outsiders many of whom may deserve to be harmed? Remember; when Martin Luther King fought segregation in the 1960's, there were plenty of racists who were harmed when he succeeded in getting blacks their citizenship rights. Not all harm is bad. So to what extent are you asking me to prove?
I'm not asking you to prove anything. I was responding to your seeming desire to prove something to me. So, honestly, I'm not interested. I say that because I don't want to mislead you into wasting your time. I don't see what you hope to gain.
Further, I'm not interested in anecdotes. Anecdotes only serve to establish what is possible. I'm perfectly aware it is possible 2 people could enter into a lifelong committed relationship without a marriage certificate. That's why the law accounts for "common law marriage". Anecdotes, however, don't address the statistics for how many of those relationships will break up or in some other way cause "harm".
Neither am I interested in the relationship customs of the Mosuo (or whatever other culture you might drag up that functions without marriage). Why? Because it relates directly to the point I
have been trying to make. I realize I can't stop sex outside marriage. So, even though I don't like it, I acknowledge it's going to happen. However, I expect those who intend to pursue such things in an unrepentant manner to live outside my community. The Mosuo are outside my community.
And that's where the issue of "harm" enters. It doesn't really matter how I would define harm because no one having sex outside marriage is going to seek my help unless
they think they've been harmed. If that occurs, my position is that person has no right to demand my help (through tax-supported health care, child care, or whatever). I might have compassion on someone and decide to help them, but they can't demand help.
The only condition under which someone living in my community can expect help from me due to a damaging sexual relationship is if they are living by the rules my community has established. In my community one of the rules is that they must be married.
If you still think you have something to prove to me, you'll have to proceed under those conditions.