It’s interesting to see how people treat the concept of cultural appropriation in fiction writing and how the thoughts on how to write about other people’s experiences can differ from person to person.
In the end, I don’t really think that @Yassmin Abdel-Magied (though obviously I am guessing) is saying you can’t write about other cultures, but that you really have to do some due diligence to make sure that the cultural experiences you are writing about are genuine, and not a veneer of reality that you may only see based on your own limited experiences.
Writing deeply is a difficult process, and it takes a lot of effort, research, and genuine discipline to be a good writer. Without that, you are indeed simply trying to steal some experience you know nothing about and try to make it work in a context that is, to say the least, out of context.
If you have a hard time understanding this, just think of all the Hollywood movies that get science completely and utterly wrong. Those are the cases where laziness to just do what you want trumps how to present information with a basis of reality behind it. How annoying is it to see something that is absurdly and scientifically untrue depicted as “the truth” and we have to sit and pretend like that’s the way it is just because the movie wants it to be. The same can apply for experiences with people as well, and the same sense of slight can be felt by the people that are living in the culture daily, to have that simply taken away and mangled.