I have to agree with Quath. I think we do make the choice to accept our poly sides/natures but I know that there are some who fully choose to become poly by changing and adjusting themselves to the situation. So it is both.
The problem I have with what this person said is "or to justify sneaking around on their spouses." Now I know that some people will claim to be poly just so they can feel better about sleeping around, but poly is all about openness and honesty so there would be no "sneaking".
Life is about the journey and not the destination,
so what better way to know life
than to wander all the roads and paths set before you.