Well I had a biology book that said an organism is only fit if it passes on its genes, a monogamous homosexual couple, (without modern medical procedures) won't do so. Homosexuality is unfit as a biological process, because it doesn't pass on genes.
You want to view this from a scientific, no emotion, no religious, no societal influence, there it is, homosexuality, in humans, doesn't result in reproduction of genes, therefore unfit. Being celebate is unfit. Not having children makes you an unfit organism.
Sure I'd say that's very cold, harsh, but that's what the biology book stated, an organism is only biologically fit, if it passes on its genes.
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Marriage is just fecked up in America anyway, if there were no entitlements to marriage, the right to see your loved ones, inheritances, its partly an economic issue isn't it?
Do gay couples need a license saying their relationship is valid? Many heterosexual couples don't. If the only thing a marriage meant, was that 2 people, could live together, and only be with each other, not have relations with any one else, I don't know if most people would do it, because if they already do that, why go through the ceremony?
A marriage in this country, (and others) allows hospital visitation rights, inheritances, children rights, etc.