Threesomes or group sex. What is it that bothers people about it, not getting the attention, guilt or something else? Do you feel that most are females or males getting hurt?
I am a regular participant in threesomes with regular FWB partners. There is no commitment regarding partnerships so few chances of being hurt. To us they are nothing more than good fun. Our sex is recreational and not based on love or a commitment.
I have seen a few people hurt by witnessing their partner seem to enjoy their experience with another partner. Swingers included.
My advice is if there is a doubt about the satisfaction you are getting from your sex with a partner DONT enter into a multiple arrangement.
Buy a book on positional play and enjoy some difference in how you do it together without a threesome.
I have partaken in multiple threesomes, Swinger parties, and orgy's. I personally have never been hurt. I have seen it happen, and it's usually males who get their egos bruised and freak out.