The following is a description of what cult is:
A cult is a religious group with extreme beliefs and practices - beliefs that are often contrary to science and logic but they are believed as "obvious" truth by the cult members.
The members of cults often isolate themselves from friends, family and society and use deceptive and unethical recruiting techniques
Use manipulative methods to control the minds of followers
Venerate a human leader or leaders
Recruiting work is performed by all of the members
People are not allowed to criticize the leader, the doctrine, or the organization, or read information that is critical of the cult.
Members are trained to reject and disbelieve criticism of the cult as lies from Satan.
Members spy on one another and report improper activities or comments to leaders.
Members are taught to suppress anything which might reflect negatively to outsiders about the cult.
The doctrine is absolutist and the ideology is internalized as "the Truth."
Members are told to avoid contact with ex-members or critics, even their relatives.
Members are instilled with a deep fear about ever leaving the organization, and anyone who does depart is of the devil and sometimes severely punished.
Members are emotional controlled and warned of being caught and punished.
Disciplinary action is administered by group leaders, which may involve excommunication for such things as questioning organization policy or doctrine.
People are encouraged to sacrifice education, career and family interests to server the interests of the cult.
Advocate socializing only with other members in the organization and avoiding outsiders.
The belief in apocalypse and Dooms Day.
The criticism of Muhammad and Islam was totally prohibited and if anyone dared to question him or his decisions, Omar swiftly unshielded his sword and threatened to slash the throat of the intrepid questioner forcing him to apologize. The message was sent in a very clear tone that no one must question Muhammad and his authority. 1400 years later, the message remains the same. If you question Islam you will be killed.
Muslims are instilled with the fear of leaving Islam. This fear comes in two forms. One is the fear of Hell and of eternal punishment and the other is the fear of being caught and put to death by fellow Muslims, including their best friends and family.
Based on the above, Islam is a cult. It is the biggest and the most successful cult. It practically reunites every feature of cult. Other cults may not be cultic in some of the above points. But Islam is cultic in every way and it would be a gross mistake to number it among religions just because 1.2 billion benighted people call themselves Muslims.
http://www.faithfreedom.org/oped/sina50218.htm