More then two people sex

Why is group sex unethical for most people? Is group sex more impure then 2 people sex? Based on what? More people, more germs? LOL But the germs could be in the same number disregarding the number of people, so is not such a valid argument . Then what? Why does it make some people not feel very comfortable with the idea? Why is couple the highest way of organization LOL  sex, emotions related? Isn't this an insincerity given the fact that most people cheat each other physically or emotionally anyway? What 2 people sex and emotional connection gives that the same type of relation in more then 2 people takes away?Feedbacks and opinions on this  topic are encouraged