This is true, but chattel slavery (the type of slavery practiced in the American South) is not the only kind of slavery practiced in history. Some slave cultures (Greek and Roman in particular) allowed a real possibility of manumission into freedom, or even citizenship.

Assuming chattel (or ethnicity-based) slavery was the only kind is a failure mode in the general public.

Edit: I'm not sure where you got this idea:

the racist NA slave-owners are much less likely to do certain categories of negative things, and are actually on the higher end of the nice-slavery scale on account of them usually being too disgusted or other-negative-feelings to bother doing anything to them but the occasional light no-contact beating and lots of forced labor.

The brutality of US chattel slavery varied from place to place and time to time, but there's mixed evidence at best for genuine sympathy for slaves among the slave-owners or free folks. A lot of pro-slave court cases are successful attempts by slave-owners to punish slave-renters who mistreated the property or free bystanders engaging in destructive "vandalism".

In my model and priors, the racist NA slave-owners are much less likely to do certain categories of negative things, and are actually on the higher end of the nice-slavery scale on account of them usually being too disgusted or other-negative-feelings to bother doing anything to them but the occasional light no-contact beating and lots of forced labor.

It's hard to get estimates for beatings - there appears to have been a great deal of variation - but let's just say that racism is unlikely to decrease beatings. And American slaves were definitely raped. A lot. Sometimes because they were considered inferior - after all, if the kid is half white, they'll make a better slave, right?

Roman slaves are the ones I know most about. And while they had essentially no rights, there was no concept of them being inherently inferior - they simply had lost their freedom, whether selling it to cover debts or having it taken as spoils of war. They could not be identified visually, and if freed were the equal of any Roman. Roman slaves gradually acquired more rights as time went on.

The master's power over the slave was called (dominica potestas), and it was absolute. Torture, degradation, unwarranted punishment, and even killing a slave when he was old or sick, in the eyes of the law, slaves were property who could not legally hold property, make contracts, or marry, and could testify in court only under torture. The death of his master did not free a slave. Under the Empire laws were passed stating that a slave could not be sold to fight wild beasts in the amphitheater; he could not be put to death by his master simply because he was old or ill; if her were 'exposed', or turned out on the streets to die, his was freed by the act; and he could not be killed without due process of law. But these laws were generally disregarded, and only the influence of Christianity changed the condition of slaves for the better.

Romans were not a kindly people, but they did not often forget that a slave was valuable property. Much depended on the individual master. Vedius Pollio, notorious for cruelty, once ordered a slave to be thrown alive into a pond as food for the fish because he had broken a goblet. But Cicero had great affection of his slave Tiro. The Elder Cato tells us something about the treatment of farm slaves. He held that slaves should always be at work except for the hours - few enough at best - allowed them for sleep. Slaves were not well fed, but it must be remembered that the diet suggested by Cato (grain, fallen olives or salf fish and sour wine) was very similar to that of the poor Romans. A slave received a tunic every year and a cloak and pair of wooden shoes every two years. Worn-out clothing was returned to the slave manager to be made into patchwork quilts.

If a slave escaped, he had to live the life of an outlaw, with organized bands of slave hunters on his track. A fugitive slave was a criminal, for he had stolen himself. If he was caught, he was branded on the forehead with the letter F, for fugitivus, and sometimes he had a metal collar riveted around his neck. One of these collars, preserved at Rome, says in Latin, "I have run away. Catch me. If you take me back to my master Zoninus, you'll be rewarded".

A slave could not legally own property, but he often had peculium, unofficial possessions. Often an industrious, thrifty slave could scrape together a little fund of his own if his master permitted it. City slaves had more chance to do this, collecting tips from his master's friends and guests or receiving presents from students if he was a teacher. Sometimes a master would allow a slave to have a trade and keep part of the earnings. A thrifty slave's ultimate goal was to buy his freedom. Sometimes a slave would buy his own slave to hire out. A slave of a slave was called a vicarius. A slave's property went to his master upon the slave's death.

Slaves were often punished. The most common one for neglect of duty or petty misconduct was a beating or a flogging with a lash (called a flagrum or a flagellum). Sometimes slaves were punished by having to wear a heavy forked log around his shoulders with his neck in the fork and his arms fastened to the ends projecting in front. This is where the term of abuse furcifer came from. Minor punishments were inflicted at the order of the master or his manager by a fellow slave, called for the time carnifex(executioner). Occasionally a slave would be assigned to harder labour than he was accustomed to. Utterly incorrigible slaves were sold to be gladiators. Punishments were severe for actual crimes, always a possibility since slaves were so numerous and had such free access to their master. Nothing was so much dreaded throughout all Italy as an uprising of slaves. For an attempt on a master's life or for taking part in an insurrection, the penalty was death for the criminal and his family in a most agonizing form - crucifixion. Pompey erected six thousand crosses along the road to Rome, each bearing a survivor of the final battle in which their leader, Spartacus, fell. The word crux (cross) was used amoung slaves as a curse, especially in the expression [I] ad [malam] crucem ([Go] to the [bad] cross).

A slave might buy his freedom, or he might be freed as a reward for faithful service or some special act of devotion. A formal act of manumission often took place before or praetor, but it was only necessary for his master to declare him free before witnesses. A new-made freedman set on his head the cap of liberty. A freedman was called libertus as an individual or in reference to his master, and libertinus as one of a class. His former master became his patron. [source]

Some links:

http://www.thetalkingdrum.com/wil.html http://www.spartacus.schoolnet.co.uk/USASpunishments.htm http://en.wikipedia.org/wiki/Treatment_of_slaves_in_the_United_States#Punishment_and_abuse http://en.wikipedia.org/wiki/Fugitive_slave

Roman slaves: http://en.wikipedia.org/wiki/Slavery_in_ancient_Rome http://www.roman-colosseum.info/roman-life/slave-punishment.htm http://www.mlahanas.de/Greeks/LX/SlavesRomanEmpire.html