For me personally, I've never had much of a care for sex. Not much desire for it, and what desire I do have within me, I have only ever wanted to share with someone I'm very very close with(which is next to no one over the course of my life, but my wife fills that role now.) So honestly I'd have probably zero desire for group sex. Intimacy is hard enough for me one on one.

As for other people? So long as everyone involved is consenting, I don't think it's for me to judge. I think people should be free to pursue their desires and do what is pleasurable to them(unless their idea of pleasure is someone else's unwanted pain, of course).