Some argue for homosexual relations on the basis of justice.  John Stott examines this argument:

‘The justice argument runs like this: “Just as we may not discriminate between persons on account of their gender, colour, ethnicity or class, so we may not discriminate between persons on account of their sexual preference. For the God of the Bible is the God of justice, who is described as loving justice and hating injustice. Therefore the quest for justice must be a paramount obligation of the people of God. Now that slaves, women and blacks have been liberated, gay liberation is long overdue. What civil rights activists were in the 1950s and 60s, gay rights activists are today. We should support them in their cause and join them in their struggle.”

‘The vocabulary of oppression, liberation, rights and justice, however, needs careful definition. “Gay liberation” presupposes an oppression from which homosexual people need to be set free, and “gay rights” imply that homosexual people are suffering a wrong which should be righted. But what is this oppression, this wrong, this injustice? If it is that they are being despised and rejected by sections of society on account of their sexual orientation, and are in fact victims of homophobia, then indeed they have a grievance which must be redressed. God opposes such discrimination and requires us to love and respect all human beings without distinction. If, on the other hand, the “wrong” or “injustice” complained of is society’s refusal to recognize homosexual partnerships as a legitimate alternative to heterosexual marriages, then talk of “justice” is inappropriate, since human beings may not claim as a “right” what God has not given them.

‘The analogy between slavery, racism, the oppression of women and homosexuality is inexact and misleading. In each case we need to clarify the Creator’s original intention. Thus, in spite of misguided attempts to justify slavery and racism from Scripture, both are fundamentally incompatible with the created equality of human beings. Similarly, the Bible honours womanhood by affirming that men and women share equally in the image of God and the stewardship of the environment, and its teaching on masculine “headship” or responsibility may not be interpreted as contradicting this equality. But sexual intercourse belongs, according to the plain teaching of Scripture, to heterosexual marriage alone. Therefore, homosexual intercourse cannot be regarded as a permissible equivalent, let alone a divine right. True gay liberation (like all authentic liberation) is not freedom from God’s revealed purpose in order to construct our own morality; it is rather freedom from our self-willed rebellion in order to love and obey him.’

Stott, J., 2006. Issues Facing Christians Today 4th Edition. R. McCloughry, ed., Grand Rapids, MI: Zondervan.