This is true, but you need to consider the context of the debate. The problem with political discussions is that every person (or every side) is actually debati

This is true, but you need to consider the context of the debate. The problem with political discussions is that every person (or every side) is actually debating something else. That said, there are three common contexts to "bringing up the wrongs of the past:" 1 - It's a counter to traditionalist/revivalist/restorationist sentiment and/or mythology. In this case, the myth is that all freedoms come from and are rooted in the infallible founding. Any change is a corruption or a regression and reduces freedom. The true history is that abolition happened first in the empire. The moral change which made the term "freedom" applicable in any meaningful sense came from outside the empire. The conclusion (should be) exactly what you laid out. Freedom, and a lot of other things we value are really the result of societal progression. IMO, it's essential to make this argument. 2 - To make analogies to the present. "In the past, people thought it was OK to X. Today, we don't." 3 - It's a baid faith argument. China suppressing traditional minorities because "the americans did it." This context is just a character assassination attempt and it's bad.