How many years has this memorial stood without the need for "clarification"? And why NOW all of a sudden is this needed?

If it's so vital to do this, then we also need to update the Lincoln memorial to point out that he saw blacks as inferior to whites (see the Lincoln-Douglas debates). We can also "clarify" that Lincoln promoted a program to "colonize" free blacks back to Africa (see his support of The American Colonization Society and the origins of Liberia).  And we can also "clarify" that Lincoln had no problem whatsoever with protecting slavery in the South (see his comments on The Corwin Amendment in his first inaugural address).

Lincoln was the most racist President in our nation's history (second, perhaps, only to Obama). If Jefferson's memorial needs "clarification", then Lincoln's memorial should reflect the facts surrounding his racist words and deeds.