From Justice Kennedy’s majority opinion:
As all parties agree, many [polygamous and polyamorous groups] provide loving and nurturing homes to their children, whether biological or adopted. And hundreds of thousands of children are presently being raised by such [groups].
Excluding [polygamous and polyamorous groups] from marriage thus conflicts with a central premise of the right to marry. Without the recognition, stability, and predictability marriage offers, their children suffer the stigma of knowing their families are somehow lesser. They also suffer the significant material costs of being raised by unmarried parents, relegated through no fault of their own to a more difficult and uncertain family life. The marriage laws at issue here thus harm and humiliate the children of [polygamous and polyamorous groups].
[Polygamous and polyamorous groups] are consigned to an instability many opposite-sex [and same-sex] couples would deem intolerable in their own lives. As the State itself makes marriage all the more precious by the significance it attaches to it, exclusion from that status has the effect of teaching that [those with a polygamous or polyamorous orientation] are unequal in important respects. It demeans [those with a polygamous or polyamorous orientation] for the State to lock them out of a central institution of the Nation’s society. [Polygamous and polyamorous groups], too, may aspire to the transcendent purposes of marriage and seek fulfillment in its highest meaning.
The limitation of marriage to opposite-sex [and same-sex] couples may long have seemed natural and just, but its inconsistency with the central meaning of the fundamental right to marry is now manifest. With that knowledge must come the recognition that laws excluding [polygamous and polyamorous groups] from the marriage right impose stigma and injury of the kind prohibited by our basic charter.
These considerations lead to the conclusion that the right to marry [whomever one wishes to marry] is a fundamental right inherent in the liberty of the person, and under the Due Process and Equal Protection Clauses of the Fourteenth Amendment [polygamous and polyamorous groups] may not be deprived of that right and that liberty. The Court now holds that [polygamous and polyamorous groups] may exercise the fundamental right to marry. No longer may this liberty be denied to them.
No union is more profound than marriage, for it embodies the highest ideals of love, fidelity, devotion, sacrifice, and family. In forming a marital union, two people become something greater than once they were. As some of the petitioners in these cases demonstrate, marriage embodies a love that may endure even past death. It would misunderstand these men and women to say they disrespect the idea of marriage. Their plea is that they do respect it, respect it so deeply that they seek to find its fulfillment for themselves. Their hope is not to be condemned to live in loneliness, excluded from one of civilization’s oldest institutions. They ask for equal dignity in the eyes of the law. The Constitution grants them that right.
Now tell me, on the basis of the reasons given, why not?