Let me take a guess: There are no black slave ancestors in your family.
Yes there's a difference between the confederacy and the Nazis, but it wasn't huge. The Nazis took what was a general attitude to non Europeans (particularly Jews and Slavic communists) by Europeans (and North Americans) and turned it into an extreme "final solution". Confederates enslaved an entire racial class, ripped their families apart and condemned them to perpetual labour in the fields.
To say the Confederates weren't evil and merely wanted to control their own destiny is falling right into the white supremacist mythology of the "Lost Cause of the Confederacy"
which grew after the Civil War until it reached a crescendo around the First World War.
The political system didn't fail them. What was happening before the Civil War was a wide movement to remove slavery from the western democratic society which had swept Europe and had made massive inroads into North America until it hit hard against the South whose wealthy class was basically formed by slave-owning agricultural class which wasn't prepared to give up their lifestyle and source of income; basically cotton dollars required the continued enslavement. Remember that these are the same folks who insisted that negros count as 3/5th of a man in the Constitution, not because they thought he was a fraction of a human being (in fact they thought of negros as sub human) but because they wanted the additional numbers to bolster their political weight in the central government vis a vis the growing Northern population. That wealthy class was completely supported by the South's lower classes who were more than happy to treat slaves as their inferiors and to rally around the jingoistic "States Rights" rhetoric of the day.
Not evil? Read a book about Andersonville some day to see how the Confederacy treated white prisoners of war. Or the Confederates' massacre of black POWs at Fort Pillow.
I know that you are trying to slot this argument into a bigger point but unfortunately your point is lost on what can easily be perceived as the minimization and excusing of an attempt by the South to maintain the indefinite oppression of a race of people which even at the relevant time was considered totally unacceptable by the right-thinking, God-fearing western society of the day.