What is your problem! You are being obtuse.
If you want to know why polygamists should be given a voice at the Vatican (or anywhere) to define marriage, you should address that question to someone who is willing to defend it. As far as what I have said, your question is a “straw man.” I no more argued that polygamist should “define marriage” than I argued that the Catholic church should accommodate polygamy or same sex marriage, your insinuations to the contrary notwithstanding.
But, yes, we will have to “accommodate” polygamy. We “accommodate” the polygamy of the Patriarchs with a brief caveat: “In the Old Testament, the polygamy of patriarchs and kings is not yet explicitly rejected.” We may “accommodate” polygamists by not burning them at the stake, by not sealing their lips, by letting them air their grievances and opinions and then, when they are willing to listen, give wiser counsel. That is what I see Humanum as doing. They don’t just chatter on some strict, narrow rail. They approach the relationship of man and woman as something that goes beyond marriage,and marriage as something more profound than one man and one woman having sex together, as becomes obvious when one reads or listens to even a few of the presentations at Humanum 2014.
Are polygamists human? Can they reason? Are they not capable of love? Do they not believe in some form of marriage? The speakers addressed gender identity, how God reveals his presence through marriage, the damage to our culture and children when we reject God’s plan for marriage and sexual relations, gender ideologies, how the covenant of marriage and the conjugal relationship parallels our intimate relationship with God, and so on. There are those who believe that people with wrong beliefs should be ostracized and given no voice. I am not such a one. I believe heretics should be given a voice. How else know they are heretics? Polygamists should be given a voice. How else know which arguments to address? Why talk about the Bible to an atheist who engages in polygamy because she thinks it’s healthy? Address the health issues. Why talk to a Mormon about the health issues that come with polygamy? For them the core issue is that it is a commandment from God. To the atheist seeking health, explain the physical and psychological problems. To the Mormon seeking to do God’s will, explain God’s will.