Oh, no. People need to decide independently that they want to be in a poly relationship. Instead, in these situations men decide they want to be “poly” ie they want to sleep with other women, which is not the same as being in an ethical poly relationship. Telling your partner it’s poly or breakup is creating a coercive situation. A lot of women don’t know how to handle that. They don’t have the skills to set boundaries. Meanwhile men being men, end up sleeping with the woman’s friends and members of their shared community. It’s bad and it ends up harming the woman, not the man.
Ethical poly is awesome. But two adults coming to a decision about what they both want is very different from one person deciding what they want and bullying the other person into it.