Ages of experience have taught humanity that the commitment of a husband and wife to love and to serve one another promotes the welfare of children and the stability of society.
If we change the definition of marriage to be more inclusive, then it is logical to argue that we should broaden the definition so that won't exclude anyone.
Marriage is an institution fits in perfect harmony with the laws of nature whereas systems of slavery and segregation were designed to brutally oppress people and thereby violated the laws of nature.
