This is completely rational. When there is no standard for marriage, everything is made “right.”
Gay marriage also legitimizes polygamy and polyandry. Again, once the definition is no longer “between a man and a woman,” what is left is “everything.”
Your lack of argument is “stupid.”
My question is: where does it stop? NAMBLA would like to be next up, with the legalization of adults having sex with and marrying small children.