If white people started openly calling black people "nigger", and black people thwarted them by ignoring or laughing at them, the word would lose its power. White people use it as a weapon that makes black people explode, then they sit back and smugly admire their work. A friend of mine tells how a little white girl once called her a nigger and she laughed and stuck out her tongue at the little bitch who promptly broke down and started crying.
There are worse things to be called than nigger. e.g. motherfucker, cocksucker, son of a bitch, asshole or cunt, Nigger is a slave term that is kept alive by the knee-jerk reaction it provokes. Such is life.