This idiot overlooks an important point. Historically (and even in other cultures around the world today), polygamy has had far more legal and cultural acceptance than "gay marriage."
Anyone who deigns to suggest that polygamy is not going to follow the same road to legal acceptance here in the U.S. is either delusional or is lying. The Supreme Court didn't change the legal definition of marriage last week. It eliminated any basis for any definition whatsoever.
Could the polygamy argument come first from a Muslim? If this is accepted in their culture and we as a nation seek to accept all cultures...why not?