Polygamists are denied the lawful union of their choice. So are Joe and his cousin Sally (the health reasons are not substantial enough to forbid this). And my roomate and I, who are heterosexual but choose not to marry becuase we like the bachelor lifestyle, are being deprived of tax benifits, visitation, inheritance rights, and societal recognition.
Fact is, I am not being discriminated against because other men and women get married. If I was homosexual, i would still not be getting discrimated against.