I think you're very right about different perceptions of time. I have an anecdote. My brother once hosted a team of youth soccer players from England. We were driving in a van though town one day and he thought he'd mention some local sites of interest. He pointed at a building and proudly said "That building is over 150 years old!" The kids were clearly unimpressed, one of them muttering something like "There're a couple of churches in our town over 1,000 years old".
What you said may be true for Europeans, but wrong for Americans, and the reason is - the Atlantic Ocean. We live in spacetime, so geography is a factor also. I think we Americans have a sense of disconnectedness with world history simply because of the physical space between the Old World and the New World. I know Jews don't refer to the Old Testament as the Old Testament, and I don't know if Europeans refer to themselves as the Old World, but the fact that we use the terms is perhaps some evidence of what I'm saying.
I believe men do feel a connection with the land they live on, even if subconsciously. Europeans live on a "historic" land, i.e., you have much of the writings, ruins and artifacts which the men of those lands produced. America began on a land which was still "prehistoric" in a sense. The past of our land is murkier.
And some of the disconnectedness was intentional, as reflected in the earliest political thought which strongly encouraged non-interventionism. They knew European history with all its complicated entanglements and bloody wars, and said "we want nothing to do with that, we can be a blank slate, we're starting something new".
So since your main point is about slavery, which occurred on American soil, I guess nothing I just said is relevant. My apologies for that, but I thought what you brought up is interesting in itself.
I agree to an extent that a society and its history are bound to each other, but history does not
determine society. We are individuals, and groups of individuals, who make free choices. I couldn't find it when I searched just now, but many years ago I came across a Fiji web forum. There was a thread where Fijians were discussing how they should feel about their history of cannibalism. The responses varied widely from "We should feel horribly ashamed" to "It's nothing to be ashamed of. It was the cultural norm of the times" to one gentleman who said "There's nothing wrong with it. I think we should still eat people today."

So, as I say, individuals make choices. And part of making choices is picking and choosing what influences you. The French still celebrate Bastille Day. They may be right to be proud of that event, but there are other events of the revolutionary period which I'm sure they do not celebrate.