the honoring and preserving of the CSA imagery and heroes with their statues and monuments was probably necessary in preserving the Union after the Civil War. I can see the politicians doing what they could to appease and sooth the defeated South.
It wasn’t necessary, but it was expedient. I’m prepping a course on post-Civil War US history and have been working on the Reconstruction unit this past week. The work of Eric Foner (on Reconstruction) and Gary Gallagher (on the specific issue of Confederate commemorations and monuments) is quite illuminating on the subject.