I do not know how many African or European cities you visited, but in the ones I did (Johannesburg, Nairobi, Pretoria, Port Elizabeth, Cape Town, not to mention most major European and a few Asian cities) I did not see many assholes blasting their noise in the faces of others. In fact, the custom of young people keeping their mouth shut in the presence of elders unless asked to speak is still strong in Africa.
You seem to be confusing two things - being an arrogant asshole that spills its shit all around without any regard of others -which I find to be quite widely spread in the US, and the aesthetic preference for different music genres. One may or may not like hip hop, or any other music genre, but that totally different form someone else blasting noise into other people's faces, regardless of what genre that noise is.
Respecting other people's boundaries seem to be the foundation of any civilized society, but then US, or at least its big chunk, seems to be anything but a civilized society.
Wojtek