Many of the monuments were placed after Reconstruction and thru the 1920s. The era of the KKK, lynchings, Plessy v. Ferguson (separate but equal), and Jim Crow. No surprise the monuments to the white traitors were placed in public squares, near courthouses, etc. The message? Stay in your place n*****, the white man is in charge. 

The confederate flag became popular in the 1960s as a sign of resistance to the push for civil rights legislation, integration, voting rights, etc. 

Certainly, some memorials of ordinary confederate soldiers were put up by family as they began to die in the decades surrounding the turn of the twentieth century.

But, the bulk of these statues were, and are, meant to perpetuate the evil of slavery and discrimination. The proponents today are no less repugnant and evil than those who were fittingly crushed in 1865.