We now have laws to ensure that something like the Holocaust does not happen again.
Really? What laws exist now that didn't exist before? Have there really been no genocides since? Or does your description of it as "the first" incidence of industrial mass murder indicate that in fact there have been others since?
Something like slavery and segregation we now know is terrible could happen all over again if we didn't know the effects from the first time it happened.
Yes, because America is now blessedly free of segregation, and no longer has schools and neighborhoods that are essentially all black or all white . . . oh, wait, never mind.
With history we know what works and what doesn't.
Exactly. Genocide, for instance, clearly works. Compare how much more stable contemporary American society is as a result of the European settlers' genocidal treatment of the Natives to how unstable Israel's situation is because they insist on containing, rather than exterminating the Palestinians. Clearly the lesson is that it is better to eliminate a people you are going to displace . ..
Okay, I'm being deliberately provocative, but my point is that your essay lacks any real depth. Your examples are generally trite and overused, and you seem to have no awareness that history is largely a tapestry of fictions put together by those who hope to influence the future by the way they describe the past. Worse, you completely miss all of the wonderful tensions and ambiguities that arise as people try to make sense of history by reviewing varying accounts of it, and that make the subject so fascinating.