Chiming in a bit late to the discussion, I know, but I have to say that I don't believe that poly people naturally have more integrity than monogamous folks.
I have seen some horribly abusive, manipulative and downright mean behaviours perpetrated by people who self-identify as poly. I have seen lying, emotional blackmail, and jealousy used by some.
So while this may open up one aspect of integrity, it most certainly doesn't seem to do much for the others...
I think that there is a part of the poly community (and I don't mean any folks on this forum) who "do poly" because they quite frankly weren't very good at monogamous relationships. Then there are others who, for whatever reason, couldn't find a decent monogamous partner, so "settled" for becoming someone's secondary, while resenting it all along.
There are many doing poly in an open, honest way, full of integrity. That applies also to monogamous folk. I really don't think poly folks can claim any "high ground", though, when it comes to personal integrity.
"Listen, or your tongue will make you deaf." - Native American Proverb