"Of course the welfare of our children is a legitimate state interest. However, limiting marriage to opposite-sex couples fails to further this interest. Instead, needlessly stigmatizing and humiliating children who are being raised by the loving couples targeted by Virginia's Marriage Laws betrays that interest. E. S.-T. [the 15-year-old daughter of two of the plaintiffs], like the thousands of children being raised by same-sex couples, is needlessly deprived of the protection, the stability, the recognition and the legitimacy that marriage conveys."