I don't think the issue is hetero relationships. The issue is monogamy which is an inherently patriarchal construct which posits men as leaders of the relationship and women (and children) as followers, where the partners own each other, and men in particular, own women.

Opening up my 20+ year fairly happy and I thought egalitarian relationship to other lovers and loves broke open a Pandora's box of subconscious beliefs and roles that we didn't even realize we had bought into until we made the conscious choice to challenge them. Poly only works when those involved do the work to deprogram themselves from monogamy mindset and begin to take real responsibility for their emotions and their lives, but when that takes place, it can be amazing!