It's always interesting to see people get het up about such things. I recently debated Ben Sledge on the issue - he has the same concerns as you, and I am non monogamous. I suspect you'd enjoy the exchange of ideas.

This is me https://medium.com/p/89f54aec158d - but Ben's piece is linked inside it. I believe people who disagree should do so intelligently. I think you're wrong about this issue - but most of my arguments are contained in there, so I shan't repeat myself too much. :o)