Kill? I wouldn't go that far, but sporting a Confederate flag patch would definitely bring a bunch of dirty looks anywhere inside a large city. Might even result in fisticuffs or a loud confrontation.
I still see folks sporting the stars and bars here and there, but I live on the outside edge of Dallas County.
I don't think it is unusual for 30 or 40 people to be shot down on the streets of Chicago on a long weekend - and for doing a lot less than flying a Confederate flag. Sometimes it is over a 75-cent bet.
If there were reports of someone flying a Confederate flag in Chicago, I wouldn't be surprised if a hundred people weren't shot down in 12 hours.
The toll would probably be less in a third-world type city in the South. But maybe not.