The Nation of Islam is not considered to be a truly Islamic organization by whom? I know a guy who is a "mainstream moderate" Muslim but he respects and admires Farrakhan and the NOI. I would suspect that he is not alone in his views. The NOI sees itself as being part of the "Muslim Nation." I don't see the NOI being criticized or condemned by CAIR and other supposedly "moderate" Muslim organizations.
Some time when you get a chance check out the "Black Moslem" and "Hanafi" murders in DC back in 1973.
That's set the stage for inter/intra Islamic criticism in the United States for the past 34 years.
Fear works you know.