If the flag of an armed enemy of the U.S. is allowed to fly over government buildings, then it implies that slavery, or at least the threat of slavery, is sanctioned by that government and can still legally exist.
“I want you to know what I have told Australia's Parliament in Canberra - what I told General Petraeus in Kabul - what I told President Obama in the Oval Office this week. Australia will stand firm with our ally the United States.”