First of all, not even the native english speakers here are all "(us-)americans".
"Acting as a black" has historic roots in blackfacing which is widely seen as derogatory, at least by black people. There is a significant power gap between black and white us americans and its just very bad style for the group in charge to pose as the other.
If a white acts like their (black) peer group and s/he does it out of respect and perhaps even admiration, the black folks will usually see it the way its meant and roll with it. If its done for following a trend and acting cool, it will be seen as a cultural rip off. As far as I can tell, theres more white folks who have a problem with Iggy than blacks.
"Acting as a black" has historic roots in blackfacing which is widely seen as derogatory, at least by black people. There is a significant power gap between black and white us americans and its just very bad style for the group in charge to pose as the other.
If a white acts like their (black) peer group and s/he does it out of respect and perhaps even admiration, the black folks will usually see it the way its meant and roll with it. If its done for following a trend and acting cool, it will be seen as a cultural rip off. As far as I can tell, theres more white folks who have a problem with Iggy than blacks.