I think there's a difference between gradual cultural blending due to regional/cultural/language proximity, such as what you're describing, and say me, getting a religiously significant Hindu tattoo just because I think it looks cool when I know very little about Hinduism, am not personally invested in Hinduism, and have no intention of converting to Hinduism. There are lines, they're just blurry.
But when we go back to the original cultural appropriation of Rock and Roll, we often see that's the same thing that happened there. Regional, cultural proximity. Here's the wiki article quote on the orgins of rock and roll. The migration of many former slaves and their descendants to major urban centers such as St. Louis, Memphis, New York City, Detroit, Chicago, Cleveland, and Buffalo (See: Second Great Migration (African American)) meant that black and white residents were living in close proximity in larger numbers than ever before, and as a result heard each other's music and even began to emulate each other's fashions.[21][22] Radio stations that made white and black forms of music available to both groups, the development and spread of the gramophone record, and African American musical styles such as jazz and swing which were taken up by white musicians, aided this process of "cultural collision".
I fail to see the point you're making. Rock and Roll and Jazz are both artistic and musical movements. They're neither, in my opinion, signficantly religious or culturally iconographic (though I will admit that religion has affected both forms of music and that they're iconic of black culture in a way, but not iconic as in "this static image represents black America"). I'm also completely aware that regional, cultural, and linguistic proximity leads to blending, acknowledge that, and am not disputing it. The original point I was making, is that beyond things like art or clothing or music, is that religion has a deeply personal value to people of all cultures and that I think its understandable that many people think it's important that others be respectful of the significance of belief systems that to them are very profound. I'll also say that I'm well aware that the sharing of and blending of religious beliefs is very much a part of every religion and plays a role in the development of religious thought and philosophy throughout history. Once again though, I think it's important to point out that a large part of that sharing is through proximity and an admiration of the viewpoints of others, and that there is a difference, but the lines are blurry.
I think a good example of that would be the swastika for cultural appropriation. You'll see it all the time in Asia still because they don't associate it was Nazi-ism, but instead with Buddhism. Clearly it does damage. But I don't feel that religion has any special significance above any other form of culture.
The swastika would go back to my point of appropriating a symbol with significant meaning could devalue that meaning. Now to a large number of people, instead of it meaning something auspicious and good, it means something hateful and sinister. I think we're only in disagreement as to whether or not religion should be treated as a sacred cow (heh.)