A biblical critique of slavery

It is often supposed that the Bible accepts without question the institution of slavery. The implication is, of course, that the Bible is wrong, and that we now know better.
But does the Bible itself contain a critique of slavery? Ian Paul thinks so, and offers the following texts for consideration:
Creation
Genesis 1:26f – God created human beings in his own image. ‘In contrast to other ANE texts, there is a universality here to the image of God in humanity; it is not confined to one sector or class of humanity…This foundational text…offers a critique of any system which seeks to divide different groups of humanity into fundamentally distinct categories.’
God’s ownership
Lev 25:23; Psa 24:1 – All things belong to the Lord; human ownership is always provisional. This principle applied to slaves, who were to be liberated at the time of Jubilee.
Rights of slaves
Ex 21:26f – This and various other regulations set out the rights and protection of slaves. Elsewhere in the ANE slaves were treated as chattels; in the OT they are to be treated as human beings.
The Exodus as deliverance from slavery
Simply put: the Lord is a god who sets slaves free.
The universal invitation of the gospel
From the beginning, the Christian movement included slaves as well as free people. It is pretty clear that they participated fully in Christian gatherings. According to 1 Cor 12, all believers are gifted by the Holy Spirit for the common good.
Paul calls himself as ‘slave’ – and Jesus Christ too
Paul was a ‘doulos’ of Jesus Christ, and Christ himself took the form of a ‘doulos’ in his incarnation. We, too, having been slaves to sin, have become ‘slaves of God’ (Rom 6:22).
Ethical language about slaves and masters
In the various household codes of the New Testament, slaves are addressed directly, and appealed to as ethical agents.
‘The scope of the power of masters is strictly limited, not least in the light of the fact that all, slave and master, have one Master in heaven to whom they are both accountable’ (Eph 6:5-9). While, on the one hand, this text appears to accept slavery, it contains a radical critique of the underlying assumptions of the institution in the 1st century Roman empire. In Col 4:1, masters are instructed to treat slaves with ‘equality’. And Paul appeals to Philemon to receive back Onesimus ‘no longer as a slave, but as a brother’ (Phile 16).
Slavery and sexuality
It is to be noted that the texts on sexuality do not embody this kind of critique. They are ‘consistent and unambiguous in their affirmation that marriage and sexual union is between one man and one woman. The nature of the texts, the later debates in the church, and the theological issues at stake are quite distinct one from another.’