Thank You for a fine post. Often in the course of any discussion of racism the social customs and common attitudes of the entire nation are overlooked in order to condeam just the southern people.
You are correct, Robert G. Shaw was NOT held in high regards among his fellow officers because he commanded a Black regiment. It was thought that Blacks would not fight, and that is what Shaw set about to prove Wrong. Those were the attitudes of the Northern army. The whole point of the 54th Mass. at Fort Wagner was to disprove Northern bigotry. But the discussion centers on the "disrespect" of the southerners in burying those dead, rather than the "disrespect" of the northern commanders that caused them to make that charge in the first place, and without proper support.
Sort of like the Pot calling the Kettle black. It like Granny said; Before condeaming someone else, you need to sweep around your own doorsteps and make sure your own house is in order first.