Their whole cuckoldry kink feeds into exactly the crap that many of us have discussed in the threads about being fetishized, having an obsession, etc. And I think Ra is onto something when he mentions entitlement. The essence of that thing is the notion that the ww and the bm are there to perform for the wm's voyeuristic pleasure. The ww wife is "allowing" herself to be trafficked, placed on display in her most intimate of moments, feeling pleasure with a bm, yet the wm's presence makes it all about him. Soooooo reminiscent of Eldridge Cleaver's writing on the supermasculine menial, the hyperfeminine female and the omnipotent administrator. It's repugnant.
Everyone has a right to enjoy their sexuality in whatever way seems best to them, provided that all involved are consenting adults. I just wish that their "tastes" didn't have such wide societal purchase, or potential ramifications for others to deal with.