Because many of us had Christianity forced upon us as children. Most atheists don't care, though...you're only talking to the ones that WANT to debate. It's not about getting angry. I just don't get how you can worship and make excuses for anything that DEMANDS worship after killing millions of innocent children. A god that endorsed slavery, which actually lead to millions of people being enslaved.
Do you believe it is ok to own another human?
So, in the Old Testament even slavery was seen as servanthood rather than servitude. Slaves / servants could go free after 7 years if s/he wanted . In the New testament as Christ has taken all our sins on to Himself and gets all the blame, punishment for those , the ' law' of love should operate as Christ gave His life for all. OK mate, you sin like rest of us. You're not sinless. Just like the rest of us. Jesus made the old law , new and complete . Just try to bear this in mind as I go on to answer this great issue you bring on.
So in Deuteronomy 24:7 (ESV): 7 “If a man is found stealing one of his brothers of the people of Israel, and if he treats him as a slave or sells him, then that thief shall die. So you shall purge the evil from your midst.
Deuteronomy 23:15–16 (ESV): 15 “You shall not give up to his master a slave who has escaped from his master to you. 16 He shall dwell with you, in your midst, in the place that he shall choose within one of your towns, wherever it suits him. You shall not wrong him.
Human trafficking ( modern slavery ) is the recruitment, transportation, transfer, harboring, or receipt of a person by the threat or use of force, fraud, deception, or coercion, or the giving or receiving of unlawful payments for the purpose of sexual exploitation or forced labor. There's a lot of it about.
God sees them as victims of a crime. Slavery is illegal in every country of the world, although some countries enforce the law less or more than others. In many cases, trafficking involves some kind of kidnapping, which was punishable by death in the Old Testament (Deuteronomy 24:7) see above, and identified as lawless, rebellious, and ungodly in the New Testament as 1 Timothy 1:9–10 says: " understanding this, that the law is not laid down for the just but for the lawless and disobedient, for the ungodly and sinners, for the unholy and profane, for those who strike their fathers and mothers, for murderers, 10 the sexually immoral, ENSLAVERS , liars, perjurers, and whatever else is contrary to sound doctrine,). "
Slavery was allowed and supported by the civil authorities in the time of the New Testament, and Paul did encourage slaves to submit to their masters and the system (Ephesians 6:5–8; Colossians 3:22–24), knowing that, if they didn’t, they faced branding or execution. But since slave owners no longer have the legal right to own slaves, these exhortations become largely irrelevant .The biblical ideal for slavery is the eradication of slavery.
In Old testament every 7 years a slave could leave and become free. Nowhere else was that practiced except in the days Before Christ in Israel.
We see this in leviticus 25 and Deuteronomy 15 . No Israelite may become a slave. All Israelites are servants of God. God took the people out of the House of Bondage in Egypt to be free, not to be slaves. Just as the earth is the Lord’s and is not ours to possess, so all Israelites belong to God and may not be possessed by other human beings, not by other Israelites and especially not by non-Israelites.Leviticus is very clear.
Racist slavery was practiced by 'Christians' around the time of colonisation which many nations are guilty of and that is a certain blot in their copybook. It actually continued worldwide and it still happens today. Those who didn't repent of their deeds certainly made a mistake and will have met their maker by now. That frightening fact can't be under emphasised. But Christianity is a fulfilment faith and William Wilberforce knew and believed that Christ hated it because we are all made in God’s image. Jesus said " do to others what you would have them do to you' which is the golden rule. He said we "should turn the other cheek " in non retaliation - love of neighbour as love of self - There is no room for abuse or control of anyone in Christ's teachings which fulfilled( completed) the Torah Old Testament . We also see so much of control slavery right now in governments and media worldwide .
Some people categorically condemn the Bible because it does not call for the universal abolition of slavery. What they don't understand are the cultural conditions that made slavery a sad necessity. Even so, this was not chattel slavery—masters did not "own" their slaves' humanity; they leased their work. Like divorce and polygamy in the Old Testament , slavery was never in God's perfect plan. But, because of sin, for a time and place, slavery was permitted by God, with certain restrictions. Now , in Christ it is not permitted in any way ,shape or form.
So Wilberforce as a Christian campaigned and succeeded to have it stopped in Britain.
Jesus is clear that caring for the naked, the sick (trafficking or slave victims suffer from a wide array of illness and injury), and the imprisoned is the equivalent of caring for Him
Matt 25 :35 - For I was hungry and you gave me food, I was thirsty and you gave me drink, I was a stranger and you welcomed me, 36 I was naked and you clothed me, I was sick and you visited me, I was in prison and you came to me.’ 37 Then the righteous will answer him, saying, ‘Lord, when did we see you hungry and feed you, or thirsty and give you drink? 38 And when did we see you a stranger and welcome you, or naked and clothe you? 39 And when did we see you sick or in prison and visit you?’ 40 And the King will answer them, 'Truly, I say to you, as you did it to one of the least of these my brothers, you did it to me.’
And to reject those in need is to reject Christ (Matthew 25:41–46).
Then he will say to those on his left, 'Depart from me, you cursed, into the eternal fire prepared for the devil and his angels. 42 For I was hungry and you gave me no food, I was thirsty and you gave me no drink, 43 I was a stranger and you did not welcome me, naked and you did not clothe me, sick and in prison and you did not visit me.’ 44 Then they also will answer, saying, ‘Lord, when did we see you hungry or thirsty or a stranger or naked or sick or in prison, and did not minister to you?’ 45 Then he will answer them, saying, ‘Truly, I say to you, as you did not do it to one of the least of these, you did not do it to me.’ 46 And these will go away into eternal punishment, but the righteous into eternal life.” There is the warning to governments and individuals.
Christ isn't the enemy here.
There is nothing that needs to change in the life of a slave victim before she can accept the love of Jesus ,Yeshua. It is personal between us and Him. All of us are not perfect , not even victims or those in the trafficking industry 70% of whom were once victims, but Christ Christ was. So He can dismiss our case as the perfect Judge John 3:36 says (ESV): 36 Whoever believes in the Son has eternal life; whoever does not obey the Son shall not see life, but the wrath of God remains on him".
Romans 5:8 "but God shows his love for us in that while we were still sinners, Christ died for us."
The slave and the enslaver ultimately need healing. God is ready to accept him or her and start the healing process. He has already gone to the greatest length possible.
We all have responsibilities to fight against human ownership of people. But we must also see the sickness of our own sinful ways and turn to God.
As for anger , the atheist in general hates Scripture because it shows a perfect moral Standard which is Jesus , the Christ and it demands that we consider our way of life and behaviour.
By the way , since you talk about killing children are you for pro choice killing in the womb? Over 1 billion murdered worldwide in the last 50 years.