It's really a twisted straw man argument of sorts. We all know you can't actually change the factual realities of what has already taken place. We can't dispute that point. So, because they know you can't dispute that, (whether consciously or not) they intend to divert your attention from acknowledging and learning from the past and from changing your perception of the past. They make the argument about "change" when really it's about acknowledgement, etc. It's used as a type of rationalization.