The bill passed by unanimous consent in the House on March 6, 1924, and in the Senate five days later; Coolidge signed it on March 17. The bill authorizing the coin read:
Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembled, That in commemoration of the commencement on June 18, 1923, of the work of carving on Stone Mountain, in the State of Georgia, a monument to the valor of the soldiers of the South, which was the inspiration of their sons and daughters and grandsons and granddaughters in the Spanish-American and World Wars, and in memory of Warren G. Harding, President of the United States of America, in whose administration the work was begun ...
So TWO Republican presidents were honoring the (democratic) South. And I guarantee they didn't mean for slavery.