it was only really 90% based around slavery, that is true
States' rights. Slavery was the issue where it came to a head, but the underlying issue was definitely states' rights.
First of all the stars and bars is General Lee's battle flag, not the Confederate national flag.
If we're going to ban that, ban the national socialist, Imperial Japanese, and Soviet flags as well. Foreign powers that warred with the United States and were founded upon evil ideals.
Freedom of speech allows you to be as offensive as you like as long as you're not creating a public danger, yelling fire in a movie theater type thing. To undercut such a fundamental because some tribal bozo shot up a church should be unthinkable. Tyranny of the majority is still tyranny, even if the minority is tribal or whatever.