I don't know that black folks having cosmetic surgery is particularly controversial, in and of itself. Its just that in the case of the late Michael Jackson, he seemed to take it to an extreme, in which he seemed to set out not only to make himself look "better" but to entirely remake himself racially. That's what a lot of black folks seemed to think. There is a strong suspicion of this in the sectors of the black community -- which may have dissapated somewhat with his untimely death.
But I must caution you, Helga 123, this is an issue of some sensitivity to black people. During the Jim Crow era in America there were some very light-skinned blacks attempted to "pass" as white in order to escape the marginalization, discrimination, and institutional oppression that was clearly aimed at black people after the abolition of formal slavery with the Civil War and the Reconstruction period -- there was still something called debt peonage for a long time after that in the south, but that's neither here nor there for our purposes.
During the middle teens and early 1920s, the so-called Progressive Era, looks very different from the perspective of black people, as this was the period the greatest number of lynchings of black people were carried out -- with body parts of the condemned being cut off and sold for souvenirs, and families sitting beneath the gallows, picknicking as this was going on, having photographs taken and sent around as post cards, etc.
So, there was an understandably strong motivation for blacks who could to "pass." Many black people saw this sort of thing as a "betrayal" of the "race" (as you know race is a cultural construct with no scientific basis -- mankind is one!).
So its not just the nose job with Michael Jackson. Its also the apparent skin lightening. Now I saw an interview he gave in which he claimed to have a skin disease (one his whole family seemed to contract...) which caused his skin whitening. But I've seen people (both of color and white people) with the skin disease that removes pigment and they never, ever lighten in such a uniform way as Jackson did.....
Anyway I hope that historical background puts the matter into perspective for you.