There is much about Islam worthy of condemnation. I have observed on other threads that Mohammed consciously rejected the Gospel to which he undoubtedly had access--his Egyptian wife, Mary, was a Christian whom he abused for not accepting his false teachings. Thus Islam at its root is antichrist as the Holy Apostle and Evangelist John the Theologian used the word in his epistles. Mohammed copied what he liked about the traditional Christianity of his day--head scarves for women, prostration during prayer, some reverence for Jesus of Nazareth--to strengthen his lies.
Nonetheless, let us be honest in our critique of Islam. Allah is the Arabic word for God, used before Mohammed by Arabic speaking Christians, and still used in Arabic language Christian liturgies. There are some who argue that features of Mohammed's false teachings are drawn from an Arabian pagan moon god, but to say "Allah" is this moon god is absurd.
Incidentally tomorrow is the feast of St. Harith and the martyrs who died with him. St. Harith was the Christian leader of a city in what is now Yemen, who, with most of the citizens of his city were martyred by Arab pagans in 524. The city was retaken by the Ethiopians with assistance from the Empire, and was a pilgrimage site until its churches in honor of the martys were destroyed by the Muslims. (More proof that the attempt to credit Mohammed with giving the Arabs monotheism is a lie. He corrupted the Christian monotheism they already had.)
Thy martyrs, Harith and his companions, O Lord have received from Thee crowns of life and incorruption, for armed with Thy strength, they vanquished the tyrant and overcame the demons' strenghtless presumption. Wherefore by their intercessions grant our souls great mercy.
--the Troparion of the St. Harith and his companions
Wonderful addition to the discussion here. There's always something to learn. I had read that there were Nestorian Christian, Syrian Orthodox, and Jewish presence throughout the oases of the Arabian desert (after all, we know from history that Mohammed's first public act was to massacre the 600-900 Jewish men of Medina and enslave their widows and orphaned children, so it is absurd to claim that 1) (as you pointed out) the "prophet" Mohammed had anything to do with bringing monotheism to Arabia or 2) Mohammed "respected" Judaism and Christianity. He simply invented a new religion and used the force of arms to spread it; and had Islam never been invented by men, I believe that all of Central Asia, the Middle East, Asia Minor, and northern Africa would (STILL) be a wonderful melting-pot area of Christianity, Judaism, and native religions -- as they were before the massacres of the Islamic invaders.
Thanks for the hagiographical lesson.