How exactly?

“I commemorate my ancestors who fought and died I therefore agree with their politics?”

Poor young men getting told to fight and die under false pretences seems worthy of commemoration to me.

Do you go around on the 4th of July saying that the Union flag, the founding fathers etc were all slavers and they should be ashamed for taking pride in their heritage as Americans?

Do you tell the French about how their flag was made by violent revolutionaries who executed thousands?

It’s not the case that North= Anti-Slavery, anti-racist and South= Slavers, racists. At its peak a little more than 1% of Americans owned slaves so the people they’re commemorating had less to do with the slave trade than Axis armies had to do with the holocaust. Are you opposed to Germans commemorating their war dead? Perhaps you’d like to know how the German military still call their Air Force the Luftwaffe and use Iron Crosses on their vehicles, which surely you must find very problematic.