I think Ciarente has a point
Most of human history woman were not much more than property of a man, no one was considering that if their man raped them that it was rape and and so on.
Does from that follow that the same is true for all societies that know marriage between man and woman?
I hope current societies - well, some of them at least - show that those things can change.
If it is true that - even though all human societies up to a certain point in time treated the wives of men like this - it is not true anymore for all societies, than it follows that the same principle has to be applied to slavery:
The fact that many societies had no fuzz with what the slave-owner did with his slaves doesn't mean that a society in the future will treat slaves just the same way.
As Esna argued in the "
Mercedes thread" it is quite probable that sex with slaves is seen as counterproductive to the goal of slavery as seen within the Empire.
As Casiella said there: if the purpose of slavery is enlightenment, then rape does not have a place in the arrangement. And the stated purpose of slavery within the Empire is enlightenment of the slave.
The people who are eligible of holding slaves within the Empire are a minority to begin with and thus they are easily monitored.
If we think of slavery as something not unlike our modern systems for keeping criminals, processing immigrants and caring for disabled people - all systems where people exert control over others, are in positions of power that can be abused - and we ask, if and how many of the people that are in power there do abuse this power for their own gain and abuse their charges - be it prisoners, immigrants or the disabled - I sincerely hope that the answer will be that most civilized modern societies have found mechanisms to keep that from happening or at least to reduce it to a minimum.
Why then should the Amarr not be able to have found such mechanisms? Because earlier cultures holding slaves didn't? That's really as good as denying humans the ability to make (ethical) progress. By that very logic we should expect men to rape their woman and no one caring for it in our societies.
That argument that Amarr do it because "the Romans and Americans did it" does just not click.