Its a flag. Nobody should care what flag someone decides to fly. Let them do their own thing in whatever they see fit and you can just ignore it / look the other way. Some people legitimately fly the confederate flag and aren't at all tribal, they just oppose federalism or want to express traditional values and they have every right to do so.
America used to condone and institutionalize slavery as a common practice, made laws allowing people to own slaves, kill slaves, etc. etc. The historical context behind the American flag is just as bad as the confederate flag, so if you really didn't like the confederate flag you wouldn't like the American flag either. I personally don't salute or fly the american flag for that exact reason but I also don't crucify people who do, because some people see it as a symbol of democracy, freedom or liberty.