We already have laws that govern who can get married, e.g., against incest, age restrictions, polygamy. etc. So if marriage becomes something that anyone can define, why should these other current restrictions remain? This is a slippery slope and it goes against basic human nature and biology.
You mean bi-sexual Americans,gay Americans,Trisexual Americans, etc., etc. its just more BS. All people should come under the same rules and we need to stop making special laws for special people and treat everyone the same.