Very few people, anywhere, recognize the Stars and Bars.
If someone were to wear the familiar Confederate battle flag or rectangular Naval Jack, then yes, a terrorist mob might kill them. It would be like throwing a banana into a monkey house.
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.