That's the flip side of the point I'm not doing a good job getting across. As you correctly point out just because it's not slavery doesn't make it good. What I'm saying is that just because it is slavery doesn't make it bad. We need to judge the rightness of the situation based on the actual conditions and treatment of the workers, not the label.
As to the Roman slave system, perhaps you know more about it than I. I did not understand it to be all that egalitarian. There was a major slave uprising in the first century BC that nearly toppled Rome. Tens of thousands were killed and all of the captured slaves crucified. It sounds to me like they did not especially enjoy their condition.
A few things to keep in mind on the Roman slave uprising. First it was primarily gladiators, which was a totally different and really bizaar subsection of Roman slaves. Non-gladiator slaves were involved but they were basically joiners in the movement not instigators (and given the way the gladiators had mopped up the Roman Legions they encountered early in the uprising we have to question just how many of these late joiners were following the change in the winds, allying with the people that it looked, for a while, might actually become the new government of the Roman Empire; nobody wants to be first against the wall when the revolution comes). Also keep in mind the American labor movement in the late 19th and early 20th centuries, again like so many other things, the workers deciding they had simply had enough and resorting to violence to settle debts with their employer is not limited to workers that bear the lable of slave.
I wouldn't go so far as to call Roman slavery egalitarian, by today's standards it was brutish and cruel. But I think it's worth noting that at least some Roman slaves felt they had a better life than Roman wives. By today's standard 19th century factory work was brutish and cruel (or Mexican shoe factory work right now). Times change, society progresses, people aren't willing to put up with as much as they once did. Judging the reality of one time period by the values and standards of another will give you some very odd results.
That we can agree on.