I think you're right, using incorrect terminology to hide the truth adds the crime of hypocrisy to the crime of slavery.

Society tends to go through a form of evolution similar to that of humans - the society form itself must be able to get reborn (rennaissance) or not fall, and the societies that don't fall or are good at getting reborn aren't necessarily the least cruel.

As for your comparison to gladiatorial games - much of modern sport, where great number of people ruin their lives with anabolic steroids and similar, and where we have boxing and karate etc. as a form of legalized violence, is things comparable to gladiatorial games. In fact, it's often claimed that sport as it exists today sprung just as much from the practise of gladiatorial games as from the slightly less violent Greek Olympic games (but even the Olympics had some quite violent "sports").

Slavery exists still to this day, both labelled as slavery, and labelled as "the right to have a work".

Genocide is a practise that modern man has gotten more and more fond of, as a "tool", especially in situations where overpopulation or economical crisis brings starvation and "Malthusian disaster". It is not strange, considering that in the short term, society forms which cause Malthusian disaster are more successful, than societies which keep their population numbers down and keep great margins. Roman dominance over Carthage had partly to do with population numbers, and the dominance of "civilizations" over so-called primitive "hunter herds" with small population size and almost no weaponry, has come from this. It's not strange that today the only hunter tribes that have survived are living in inpenetrable rain forests or distant almost inaccessible islands. Of course, the more aggressive these tribes would be, the greater chance of surviving against modern civilization they would have had. Odd then, that most conserved hunter tribes are much less violent than any more "advanced" societies.

The basic problem is that society is too complex and uncontrollable. Even a saint wouldn't be able to create a better world by working through the current institutions, commissions, and so on. The society form is built in a way that makes it vulnerable to random events and forces people to act in ways that in theory seemed good, but in practise leads to the unfolding of chains of actions that cause unforeseen trouble. It's my opinion that most disasters of our time happen only because of mistake, because of accidents, and not because of malevolence. And we have created institutions that put the full responsibility of such accidents on single human beings, who acted in ways they were trained to, and forced to, do. As such, whenever any criticism is to be directed towards bad things, there will always be innocent people who will feel the criticism is directed towards them, and they will "defend themselves" against it. The result is that we also create a strange tabboo on at all criticising, even though it wasn't anybody's idea to create such a tabboo. Society forms survive if they are complex enough to make it unable to remove them and fix their problems, and if they make human beings fight each other and accuse each others whenever accidents happen, rather than rooting out the problems of the society structure. A paranoid conspiracy theoretic would say all bad things that happen are caused by malevolence, but overviewing society tells you that only fractions of all bad things are deliberate. Only one or two steps in long chains of accidents and unforeseeable events caused by an unoverviewable complex buereaucratic society.