This, of course, was the unspoken thought behind your suggestion. You just don't think that the subject is important. American chattel slavery is both unbelievably important and unique in the history of the world. To minimize its importance in the establishment and rise of the US, the history of Africa and Europe, or its importance in world culture is willful ignorance.
If anything, you're trying to 'minimize the importance' of the enslavement of people in practically every civilization on earth, for generations before the US was founded and still continuing today.
At the end of the day though, that's what the site owner wants, I just don't understand your vitriolic responses to people questioning it.
Hardly. People have been enslaving each other throughout the entirety of human history. To suggest that America is somehow exceptional in this regard reeks of ethnocentrism. The Arab slave trade is arguably just as important, but somehow I doubt you condemn residents of the Middle East as harshly as you do whites...