Actually having Sex is a requirement for marriage, even if actually having a baby is not. Marriages traditionally had to consummated in order to be valid. In case you think this is an unimportant point, look again to the life story of Henry VIII. For his fourth wife,
Henry agreed to wed Anne of Cleves, sight unseen, based on a portrait by Hans Holbein. However,
On Anne’s arrival in England, Henry is said to have found her utterly unattractive, privately calling her a “Flanders Mare”. … Henry wished to annul the marriage so he could marry another. The Duke of Cleves had become engaged in a dispute with the Holy Roman Emperor, with whom Henry had no desire to quarrel. Queen Anne was intelligent enough not to impede Henry’s quest for an annulment. Upon the question of marital sex, she testified that her marriage had never been consummated. Henry was said to have come into the room each night and merely kissed his new bride on the forehead before retiring. All impediments to an annulment were thus removed.
Her claim that they had never had sex was sufficient to annul the marriage.
Same sex marriage need not even be a sexual relationship at all, as clearly shown by the watered-down definitions of marriage used by the SSM-creating judges. And no one, as far as I know, has ever even asked the question of what would constitute the consummation of a marriage by same sex partners. And if that definition would be applied to opposite sex partners.