No. It's not appropriate. Fanfic should be about creative and positive interpretations of characters or stories. Content like this is more of a form of exploitation and not in line with the values that good fan - made content should uphold.
In movies, it's a rather rare occurrence as it involves extremely disturbing and non - mainstream themes. In literature, it's also not common as most works tend to focus on more positive or at least less extreme human relationships. Such a theme goes against many moral and ethical standards that most creators uphold.
Some might do it for shock value. They want to get attention by spreading something extremely salacious. Another reason could be a form of revenge, if there are some personal grudges involved.
No, it is not appropriate at all. Such stories often involve racist and sexist undertones and are a form of objectifying and demeaning individuals. We should strive to promote equality, respect, and positive cultural exchanges between all ethnic groups rather than spreading such offensive content.
Media platforms should have strict content filters to prevent the spread of such offensive and unethical topics. For example, using algorithms to detect and block relevant keywords.