I hear this a lot, particularly in arguments from the religious right. I understand that On the Jewish Question is very confusing to read because of how the word "jew" was equated with "usurer" in the 19th century leads to this conclusion - this is often used to discredit all of Marx's work.
Was he, or is this another case of misinterpretation?
Worth remembering that Marx himself came from a Jewish background, with several rabbis on both his father's and his mother's side of the family. So this is a young man (it's an early text) attacking his own culture, or ashamed of it, not some racist attacking a minority. And Marx did in this text support full civil rights for Jews, which was still controversial at the time.