“My only question is, how come Christians don’t get more vocally upset about cross-burning? I don’t necessarily mean in terms of the racist aspect. I mean, when someone burns the American flag, we’re outraged. Isn’t burning the
enduring symbol of christianity bad too?”
Wrong context. The burning cross is an ancient Scottish symbol for summoning
the strength of the clan in time of danger.
Since many Southerners, especially in Appalachia, were of Scots/Irish descent,
they developed the KKK out of what they knew, which the use of “Klan” makes
pretty obvious. For a more innocuous analog, think of the Shriners.
Many Scottish clan chiefs have, as a crest, an arm holding a cross, an obvious
allusion. http://www.clan-donald-usa.org/ See for a good example.
I recommend to you the historical novel THE FIERY CROSS by Diana Gabaldon, in
which she describes very nicely this custom as practiced by Scottish immigrants
to North Carolina around the time of the American Revolution. (It’s a damned
good story, too.)