|For an Orthodox Christian to praise and affirm Islam and the Qur'an is akin to spitting on the holy icons of Christ and His Most Pure Mother. When the Muslims invaded Tbilisi, Georgia in 1227, they set icons of Christ and the Theotokos in the middle of the bridge, and promised to spare all those who spit on the icons, denied Christ and converted to Islam. 100,000 Georgian Orthodox Christians chose martyrdom rather than deny Jesus Christ. Let us honor their memory by confessing Jesus Christ to our dying breath! (Source)|
William Kilpatrick warned in his article about the threat Islam poses to non-Muslims everywhere, depending on how seriously Muslims take the commands in the Qur'an to wage jihad against the unbelievers. We have seen Islamic jihad attacks climb dramatically in the years since 9/11/2001, with over 33,000 deadly terror attacks since then. This is undeniable evidence that there is something dark and violent at the heart at Islam.
However, in addition to the deadly threat Islam poses in this age, there exists also a grave spiritual danger for Christians who praise and affirm Islam, or who even affirm that Muslims worship the 'Same God' as we do.
- the Qur'an explicitly and vehemently denies Jesus Christ to be the Son of God, 
- presents Jesus as an apostle and prophet only,
- denies the Holy Trinity,
- denies that Christ was crucified,
- curses Christians,
- and commands Muslims to attack, persecute and kill Christians until they embrace Islam or pay the jizya. 
Therefore, whether they realize it or not, a Christian who praises and affirms Islam, Muhammad and/or the Qur'an is praising and affirming a false and militant religion which forcefully denies Jesus Christ and persecutes those who follow Him.
"If you accept this Muslim ‘Jesus’, and his ‘gospel’, then you also accept the Koran, and you accept Islam..." - Mark Durie
The most charitable possibility to consider is that some such Christians might be ignorant of what the Qur'an actually says and may not therefore realize the seriousness of their error in praising Islam. For such Christians, once they realize their error, they should repent at once and immediately stop doing so, and then issue retractions and apologies to their flock, their students, their listeners, and make sure they do not commit the same error in the future. They can reverse the harm of their false teaching and use the opportunity to educate their flock on what Islam actually teaches, and strengthen them to bravely confess Jesus Christ as persecuted Christians do throughout the Islamic world.
But if a Christian praises Islam or teaches the 'Same God' Heresy knowing what the Qur'an says, and knowing what Muhammad taught against Christ and the Church, such a Christian is not only openly committing apostasy and denying Jesus Christ, but they may very well be leading astray simple Christian believers and causing them to stumble.
A few scriptural warnings come to mind:
"Then [Jesus] said to the disciples, 'It is impossible that no offenses should come, but woe to him through whom they do come! It would be better for him if a millstone were hung around his neck, and he were thrown into the sea, than that he should offend one of these little ones'." (LK 17:1-2)
"Even if we or an angel from heaven should preach a gospel other than the one we preached to you, let him be anathema! As we said before, so say I now again: If any preach any other gospel unto you than that which you have received, let him be anathema." (Gal 1:8-9)
“But I fear, lest somehow, as the serpent deceived Eve by his craftiness, so your minds may be corrupted from the simplicity that is in Christ. For if he who comes preaches another Jesus whom we have not preached, or if you receive a different spirit which you have not received, or a different gospel which you have not accepted—you may well put up with it!” (2 Cor 11:3-4)
"Now the Spirit expressly says that in the latter times some will depart from the Faith, giving heed to deceiving spirits and doctrines of demons, speaking lies in hypocrisy." (1 Tim 4:1-2)
"Dear friends, do not believe every spirit, but test the spirits to see whether they are from God, because many false prophets have gone out into the world. This is how you can recognize the Spirit of God: Every spirit that acknowledges that Jesus Christ has come in the flesh is from God, but every spirit that does not acknowledge Jesus is not from God. This is the spirit of the antichrist, which you have heard is coming and even now is already in the world." (1 JN 4:1-3)
Mark Durie warns about the enormous differences between the Islamic 'Isa' and the true Jesus whom we learn about through the New Testament and Holy Tradition:
It is quite clear that the Injil, as described by the Koran, is nothing but a ‘different gospel’. The prophet Isa (Jesus) of the Koran is a product of fable, imagination and ignorance. When Muslims venerate this Isa, they are far removed from Yeshua, the Jesus of the Bible and of history... For most faithful Muslims Isa is the only Jesus they know.
Mark Durie, 'Which God?'
But if you accept this Muslim ‘Jesus’, and his ‘gospel’, then you also accept the Koran, and you accept Islam...
By Islamicising [the true Jesus of the Gospels, the Jesus of history] and making of him a Muslim prophet who preached the Koran, Islamic orthodoxy would destroy Christianity and take over its history...
The traditional Islamic view is that if you want to know what the God of the Bible is like, then read the Koran. Not only must Muslims believe that ‘we worship the same God’, but this message is always a central component of the presentation of Islam to Christians and Jews.
[This message] provides the lynchpin of Muslims’ efforts to convert the ‘People of the Book’ to the faith of Muhammad. In addition, this belief, once accepted, can lead Christians to support Islamic perspectives in ways other than conversion. For example, embracing this Islamic doctrine wins a measure of respect and even support for Islam from Christians.
(Durie, Revelation: Do We Worship the Same God, pp 75-76. This book is out of print, but Durie's newer book, Which God? Jesus, Holy Spirit, God in Christianity and Islam is an expanded and updated version of this excellent study.)
With all this in mind, it is easy now to see how serious a sin it is for a Christian to affirm or praise Islam, the Qur'an, and Muhammad; it is no less than blasphemy. By doing such a thing, one can even lose the grace of baptism, lose one's eternal salvation and be cut off from the Lord.
But does it mean one is "Islamophobic" or that one hates Muslims if one refuses to praise Islam? Not in the least! How absurd that would be. As William Kilpatrick so ably put it in his article,
"Critiquing Islam does not mean that one hates Muslims. Criticizing Islam is not the same as criticizing Muslims, any more than criticizing communism is equivalent to criticizing Soviet-era Russians... The distinction between Citizen X and his beliefs is a simple one. You do not have to respect his beliefs, but you should try to respect him as a fellow human being."
If anything, we ought to go the extra mile and show our evangelical love for Muslims by sharing the Gospel with them, not by praising their false religion which cannot save them. And, we must be confident of the Gospel, for Jesus Christ is the Way, the Truth, and the Life, and no one comes to the Father but through Him.
Simply put, words are important. As the Lord warns us,
"But I say to you that for every idle word men may speak, they will give account of it in the day of judgment." (MT 12:36)
"For whoever is ashamed of Me and My words, of him the Son of Man will be ashamed when He comes in His own glory, and in His Father’s, and of the holy angels." (LK 9:26)
With this in mind, let us from this day onwards vow to always bravely confess Jesus Christ as Lord, as King and God, as the Second Person (the Logos) of the Holy Trinity, of one essence with the Father. And let us not follow the apostasy of those Christians who are so quick to deny Jesus Christ and praise the forerunner of Antichrist.
 Qur'an citations denying Jesus:
The similitude of Isa [Jesus] before God is as that of Adam; He created him from dust, then said to him: “Be”: And he was. (Sura 3:59)
Say not “Trinity”: desist: It will be better for you: For God is One God: Glory be to Him: (Far Exalted is He) above having a son. . . . (Sura 4:173)
In blasphemy indeed are those that say that God is Christ the Son of Mary. (Sura 5:19)
They do blaspheme who say: “God is Christ the son of Mary . . .” They do blaspheme who say: God is one of three in a Trinity: for there is no god except One God. If they desist not from their word (of blasphemy), verily a grievous penalty will befall the blasphemers among them (Sura 5:75,78)
Christ the son of Mary was no more than an Apostle; many were the apostles that passed away before him. His mother was a woman of truth. They had both to eat their (daily) food. See how God doth make His Signs clear to them; yet see in what ways they are deluded away from the truth! (Sura 5:78)
The Jews call 'Uzair a son of God, and the Christians call Christ the Son of God. That is a saying from their mouth; (in this) they but imitate what the Unbelievers of old used to say. God's curse be on them: how they are deluded away from the Truth! (Sura 9:30)
In fact, they never killed him, they never crucified him — they were made to think that they did. All factions who are disputing in this matter are full of doubt concerning this issue. They possess no knowledge; they only conjecture. For certain, they never killed him. (Sura 4:157)
 Qur'an citations commanding Muslims to wage war against, terrorize, and kill non-Muslims, including 'People of the Book' (Christians and Jews):
Fight against those who believe not in Allah, nor in the Last Day, nor forbid that which has been forbidden by Allah and His Messenger and those who acknowledge not the religion of truth [i.e. Islam] among the people of the Book [Jews and Christians], until they pay the jizya with willing submission, and feel themselves subdued. (Sura 9:29)
Kill the mushrikun [unbelievers] wherever you find them, and capture them and besiege them, and prepare for them each and every ambush. (Sura 9:5)
I will cast terror into the hearts of those who have disbelieved, so strike them over the necks, and smite over all their fingers and toes. (Sura 8:12)
Against them make ready your strength to the utmost of your power, including steeds of war, to strike terror into the enemies of Allah and your enemies. (Sura 8:60)
So, when you meet those who disbelieve, smite at their necks till when you have killed and wounded many of them, then bind a bond firmly on them... Thus you are ordered by Allah to continue in carrying out jihad against the disbelievers till they embrace Islam. (Sura 47:4)