How do you know they don't have deep seated psychological issues and they're trying to self medicate through polysexuality?It just seems like polysexuality is a SYMPTOM of a more deep seated problem.....hate saying it....but it's true...............It's exactly the same way people sleep around and moan that they don't have any real friends or real realtionships.......When you're with someoen you honestly truely LOVE, you want to be exclusive with them. Sex is a beatiful thing, and it should be respected and not cheapened by doing it with everyone who comes down the block....
I think it's SUPER rare that a poly thing ever actually works..........Humans are far too wired to be jealous etc....One complex realtionship is hard enough to manevoer...........it's very rare for someone to be able to handle TWO complex sexual realtionships.........hell poly is just a label so they don't feel guilty about screwing with their first primary realationship.
Okay. First off-- yes, you and I do agree with sex is a natural thing for procreation, sexual pleasures, or depends on one person's personal belief. But you gotta remember that it's not everyone see that way. Sometimes, they just want to have a random sex with random people as long as it is consent
is consent.
Cheating is a mere immoral thing to do... which breaks the common sense rules. In a romantic relationship, when a woman tells a man she accepts his date request and then starts dating another man without telling either man about the other, then yes, she's cheating on both of them.
But, when a woman asks her boyfriend if she can date other people,
he agrees to it, and then she starts dating someone else, and that person also knows about her boyfriend,
that is polyamory. That means it's not cheating. As long as it is agreement, so it means contest. Polyamory involves full knowledge and consent of everyone involved. Cheating does not. Now, do you understand?
Now, as for sexual actities... Polyamory is not about sex powers or how many times they have because various people are different... Realistically, most relationships are only 3 to 4 people. Yes, some are actually more than 5 people but that doesn't mean they want more sex than anybody... As long as they agree to their contest, it will not be an issue. Sometimes, they want to wait until they're really ready. Again, people are various with different preferences...
Sure, it seems it is a "taboo" if someone have a lot of sex activities but it's her or his decision. Some people are just not meant to have a serious relationship, so you can't really expect they should be limited how many times they have.
Again, polyamory is a choice, not a crime...
All in all though, what other cups do is up to those cups. Whatever makes them happy. 
So the people who are poly, are just following their natural human wiring and desires, and not afraid to show it like 99% of the animal kingdom.... we are, animals after all.