I don’t think she was too hard on non-magical folk. If you’ll recall her descriptions of the clothing fashions and mistakes of the magical folk you’ll see she was making fun of them too.
Part of the problem is that aside from the Dursleys, very few muggles got described. In the last book, they were being punished severely, and the narrative seemed to be sympathetic to their plight.
But clearly, it is a story about magic, as is Niven’s. For those who cannot perform magic, it is as if they were handicapped in some way. In fact, the whole point of the conflict erupting in the final book was over the treatment to be accorded to the non-magical.
Why would Rowling be harsh toward non-magical folk? She KNOWS she is among us.
Why would Rowling be harsh toward non-magical folk? She KNOWS she is among us they are the ones buying her books!