Among arguments against it: Marriage is a union between a man and a woman and opening it to same-sex couples is disrespectful to religions that consider
homosexuality a sin.
Some gay people may make good parents, but same-sex couples don't provide the stability and role models of a man and a woman.
Gay rights advocates also caution that the military may take punitive action against individuals in same-sex marriages. Also, couples seeking to adopt may be barred from doing so by certain states or countries that allow adoptions by single-parents but not same-sex couples.