Srdja Trifkovic wrote in an 1999 issue of
Chronicles magazine that Muhammed was part John Gotti, part Charles Manson; in other words, a murderous psychopath. Think about the implications of holding Muhammed to be the model for humanity, which Muslims do -- the ideal Muslim must be a murderous psychopath. Early in his career, Muhammed spoke gently and tolerantly, but as time went on and he grew in power, he became more violent and intolerant in his speech and deeds. Muslims hold that his later statements abrogate his earlier -- Allah, allegedly speaking though Muhammed, changed his mind.
To be fair, Christian rulers of the 7th century were by and large a ruthless bunch, but no one holds Justinian and Theodora or any of their royal Christian contemporaries as models for humanity for all time.