Shall I list a few of the religions that have been classified as cults using this definition, down through the centuries? As can be seen by legal and mob persecution against them.
Christians, Jews, Mormons, Catholics (in Russia and elsewhere), Orthodox Christians (in Poland and elsewhere), Hugenots, Waldenses, Jehovah's Witnesses, Hasidim, Unitarians, Anabaptists, Seventh-Day Adventists, Mennonites, Christian Scientists, Quakers.
That's just off the top of my head.
BTW, I don't object to Boortz believeing Islam is a cult. I object to his stating his personal opinion as a fact. "Islam isn't a religion, it's a cult."
Maybe down through the centuries you could say that, but that wouldn’t fly for those religions today. Islam is in the same state it was 800 years ago.