From Paragraph 46: "This is not a naïve quest to solve all our problems at once.".
Why did he use it? 
I think Landrieu wanted to use this certain term for his audience to understand that even though he was taking out the confederate monuments for the sake of everyone it meant that it wasn't a mission to "solve all our problems at once".

From Paragraph 3:"You see—New Orleans is truly a city of many nations, a melting pot, a bubbling caldron of many cultures. There is no other place quite like it in the world that so eloquently exemplifies the uniquely American motto: e pluribus unum—out of many we are one. But there are also other truths about our city that we must confront. New Orleans was America’s largest slave market: a port where hundreds of thousands of souls were bought, sold and shipped up the Mississippi River to lives of forced labor of misery of rape, of torture. America was the place where nearly 4000 of our fellow citizens were lynched, 540 alone in Louisiana; where the courts enshrined ‘separate but equal’; where Freedom riders coming to New Orleans were beaten to a bloody pulp. So when people say to me that the

monuments in question are history, well what I just described is real history as well, and it is

the searing truth."
Why did he use it? I think Landrieu wanted to use this certain term for his audience to understand that he wanted people to know that so that it perfectly exempifies the unique american motto".