So, when you said:
There is really nothing "perverted" about their sexual preferences.
We can all infer that you find nothing perverted about having group sex and/or sharing wives and husbands with others, that you think there is nothing perverted about that. That's your opinion, Luis, and it's shared by tortoise and EricOKC among others here, but please allow the rest of us our own opinions about that kind of "lifestyle." However, if it is your opinion, don't deny it later on. It might bring up the "L" word, with good basis.
Ask a hundred different people, and you'll get a hundred different answers.
Some will say that oral sex is "perverted", indeed, there are laws in the books in some States making it illegal.
Others will find that a little "dirty talking" while having sex with your spouse is indicative of a perverted mind.
Some people like to have sex with the lights on, I know a more than a few people who think that is disgusting. Forget about masturbation, even mutual masturbation while engaged in the sex act with your spouse, some believe that you'll go to hell for doing that.
In fact, I know people to whom sex beyond the woman on her back, eyes closed, unduring quietly while the man "has his wey with her" is sick, and perverted.
I am certain that under someone else's definition of sexual perversion, you fall right in, I know I do.
The point here is your definition of "perverted" versus mine.
Real simple; sex between consenting adults...to each their own.
Sex with farm animals, corpses or children...you can feel free to call them perverts, and I will join you.
To me, consentual sex between adults, whether or not that sex is within societal norms (and not forbidden by civil law) does not for "perversion" make.
Sinners? No doubt...we all are.
Immoral? In this aspect, yes.
"Perverts"? I don't see them that way.