When Amber said “a song whose lyrics EXHALT THE MURDER OF SLAVES!” I went and read the lyrics and the only part that even seemed to refer to slaves is the part you posted. While it is cryptic I could not construe it to be exalting in the murder of slaves so I suggested she reread that section to see if maybe she would reconsider her interpretation.
In context of the war of 1812 (the origin of the song) “no refuge could save the hireling and slave” would seem an indictment of the British for killing non-combatants.
The song to me is an ode to the flag that represented the new nation that desired to be the land of the free and the home of the brave. The song has its flaws and taken to literally fails in some ways and I am not here to defend the anthem or the pledge of allegiance.