The problem is, which one, or group of us, decides what is evil and wrong and all of this? Everyone thinks they're the ones - their ways, cultural norms, their moral compasses, the values of their civilization, are the right ones. Well, not everyone, but most will - and based on how you're talking about this, you think you are the one in a position to make this type of judgement.
Many elements of "modernizing" and "progress" of past centuries are now looked at as horrible mistakes - barbarism and unparalleled arrogance of dictatorial mindsets, imposed on people just living their lives in what they see as a morally sound way. The people who did things like start up the Residential Schools would have talked a lot like you are right now. Same with the people who went a colonizing, going into say, India and soon to be Pakistan for economic gain, but fully expecting to civilize the savages. The people who did the evil of Westernized slavery, as you're talking about, probably talked just like you are right now Handsome. They felt justified because some things were just savage and uncivilized - just like you're thinking right now.
You're right, some things which are quite problematic get justified because of tradition or history or religion or whatever. But inversely, a lot of horrible things happen in the name of progress, of advanced civilization and more evolved moralities... In short, horrible black marks on the moral history are justified by people like you talking like you are right now Handsome. Now, we even see a lot of movements trying to capture some of the wisdom of many historical practices and teachings - the thing arrogant civilizations dubbed as savagery - because sometimes the old ways were better than what our modern sensibilities could come up with.
So, I ask the question - how have you arrived at the position where you can compare this historically precedented, globally practiced thing to Western slavery? Who handed you the gavel of absolute moral judgement which you're so comfortable swinging - and why do you deserve it? And what makes you different than the arrogant, evil men who marched into other cultures and said "ok, this is barbarism. We're going to teach you our right way of doing it - the right way of doing it"?