things to consider:

1. the "problematic" flag you are referring to is not the actual official flag of the confederate states but rather the "rebel" battle flag
2. the union invaded the south so this was the flag flown by individuals who were defending their state from a federal invasion. we need to honor and respect those soldiers they fought valiantly and in many cases more honorably than the north. the soldiers of the confederacy were not inherently bad people and the overwhelming majority (90%+) were not even slave owners.
3. the union also had slave states, the war was about "preserving the union" and had very little to do, if anything, with slavery.
4. many Indian tribes joined the confederacy including a few prominent generals.
5. learn more about the civil war it's not as cut and dry as you've been taught. it's a nuanced issue that is not just "the south wanted slavery so they started a war" as you've likely been taught. in fact, that sentence is almost 100% incorrect.
6. almost no slaves were harmed during the confederacy. in fact one of their last hail mary plans was to free and arm the slaves as a means to protect their sovereign state rights.

i'm not gung-ho pro confederacy but to act like they were 100% wrong is just completely incorrect and likely a product of a lack of research on the subject. they thought they had a right to secede legally and the war was essentially fought over that specific right.