It may be refreshing sometimes to think that slaves in America may have had advantages that those in other forms of bondage in other countries didn't have, but that can become a distorting viewpoint if one doesn't compare the conditions of slaves here with freemen in the same country. So yes, sometimes we might benefit by comparing the condition of slaves here with those of peasants elsewhere, but that is also only a partial picture.
And we may not always conclude that the slaves were better off. The answer isn't always clear. Irish or Norwegian or Polish or Ukranian peasants suffered mightily in the 19th century, but they were probably still happy about the nominal freedom they possessed -- if only for the freedom to leave. If it's the case that slaves were happier than Chinese or Indian peasants or lower castes, it may be because they lived in a richer society or because the slaves still developed a consciousness of freedom, in spite of all that had been done to them. Does this mean that it's good to be a slave in a rich society, rather than a serf in a poor one? And while America can take some comfort in promoting the idea of freedom that eventually overthrew slavery, surely it's no cause for complacency. If Brazil or Cuba offered greater opportunities for mulattos does that mean that slavery there was benign or North American slavery more condemnable than otherwise? And Africans or American Indians with their shorter lifespans and lower "quality of life," surely preferred their own lives to being slaves (though some of those Africans were quite willing to make other slaves).
I can understand the anger many have against those who want to put slavery at the centerpiece of every Civil War museum. It does look extreme and unnecessary, but when you look at some of the notions that develop when people ignore the role of slavery, it's understandable that some what to put the emphasis firmly on slavery. African-Americans felt like they were cut out of American history for a century and longer with serious consequences for their treatment during the period, so it's natural that they don't want this to happen again.
But I have to wonder what people are really arguing about. If I remember my childhood visit to Gettysburg right, there was always one display on slavery, which people didn't make much fuss either way about. I don't know if Southern museums followed such a practice then, but they must by now. The question today seems to be adding a few more exhibits on slavery that people will likewise ignore.