I see what you mean about memorials often being the end of the discussion. That is a sentiment often heard here in Germany where people see memorials as offering up a final interpretation, poured into cement. Similar terminology whenever people make a rhetorical or interprative statement that appears to be a final statement on the Holocaust - a Schlußstrich or "last word".

We also see, however, how memorials become contested sites or sites actually used for political purposes. Sometimes this comes about when a new generation comes along - as with the Forrest memorial. Sometimes the use is improvised and has only tangental connection to the content - such as the use by the Russian community of the Barclay de Tolly memorial in Riga. It serves as a marker of Russianness near the city center, so it is a kind of political rallying point.

While I agree that a museum would be better, I can imagine that a memorial might actually end up serving some kind of activist or political purpose not unrelated to slavery. In any case, I am sure the debates about its location, form and accompanying text would be very interesting.