I can't speak for everyone Pandora... but i'm willing to bet that the majority of cases (where there is infidelity due to D/s exploration) are kinky folk who have blossomed at a later time in life. A later time that may find themselves trying very hard to fit into a vanilla relationship, and now committed, perhaps with kids.
This is how it played out for me. I ignored what i couldn't understand about my sexuality, and did what everyone did. Found a very nice, attractive vanilla girlfriend and started a family. It wasn't until later in my young adult life that i realized that my monster inside was still waiting to be fed. I wish i could say it's a choice rather than a need but i can not. I continue to struggle with it daily, and i know it affects those around me.
Perhaps that why people in the D/s community tend to not frown upon it. I did enjoy your post however. Something that i still don't understand about this lifestyle is just how rampant poly relationships are here. I'm not much for poly, but nobody is saying everyone has to be like me either.. lol
Good topic..
bent