just a couple of points in summary.
1. gay couples can be afforded complete equality without calling their union a marriage. The vast majority of people want gays to have full equality under the law.
2. the gay aganda is not about equality, its abour forced societal acceptance of homosexuality as normal and equal in every way to heterosexuality (biological sexuality).
3. if gay marriage is legalized then there will be absolutely no legal defense against bigamy, polygamy, and all other forms of human groupings as marriages. gay marriage would set a legal precedent that could not be refuted.
4. interracial marriage and gay marriage are not analagous.
The essential difference between bigamy and polygamy is that the former entails the potentiality of involving another in an extended marital/familiar matrix without the other's knowledge or consent. That won't fly.
But willful polygamists can use the same line of logic supporters of same sex marriage use. One can also use the same reasoning for same sex incestuous marriages, as the prime reason for making incestuous marriages illegal, that of genetically deformed offspring, is rendered moot in a same sex marriage.
Bigamy involves fraud as an underlying crime, underage relationships have the sexual component as an existing crime. Incest does, with the exception I noted above. Bestiality based arguments are silly now, but if those PETA idiots get their way, who knows?