Actually, in many states burning a cross even on your own property is against the law, as it is considered a hate act.
I think it's Ironic that the Supreme Court, who completely messed up the "separation of church and state", managed to get itself in a position where you can burn the symbol of the country, but NOT the symbol of christianity.
It's like we have special protection for christianity not afforded to any other religion.
Note I think it's legal to burn a Koran, you just might end up dead. But the cross, that's different.