Could be my bad, but I am still not 100% clear. Are you saying that (and I know you have referred to a polyamory relationship but let's assume just a couple for the moment - and call them A & B) - are you saying if B wants to watch porn and/or have sex with C-Z, it is ultimately actually none of A's concern? What B is doing, as you said, is entirely up to you them and none of anybody else's business. If A disapproves, then I infer that you think they are doing so because of a religious root?
You seriously misunderstand the nature of polyamorous relationships. But that's okay because most people do. I'm happy to enlighten you. Any day you learn something is a good day, right?
Specifically, your use of the phrase "none of A's concern" is the problem. In a polyamorous relationship, everything is everybody's "concern". What is done is done with
consent. In your hypothetical, B is free to watch porn and have sex with other people
if and only if A consents to it. And vice versa, according to the agreement that A and B have between them. You see, polyamory
requires free and open communication between all involved. You can't be in a poly relationship if you are not actively consulting with all parties before doing anything sexual. Which is true of all kinds of relationships as it turns out.
Polyamory is not a free for all. Polyamory is an
agreement made between consenting adults. The exact nature of the agreement can and does vary greatly, but it
does not and can not work if there isn't an explicitly stated agreement in place. Any new developments must be added to the agreement before any activity can take place.
You got better when you crossed out "you" and replaced it with "them" though. The
plural pronoun. If there is a poly group, what they do within the bounds of their relationship is nobody's business but theirs.
The latter...though I have done some research now.
I'm sorry.