What is Islamic State's problem with Catholicism?

Answer 1

There is general hatred emanating from Islamic State concerning any religious group (be they Muslim or Non-Muslim) other than pious Salafist Sunni Muslims, since its goal is to rule a theocratic state based on Islamic Law where Non-Muslims feel themselves subordinated to second-class status. However, in addition to the general grievances that Islamic State has towards all religions other than Salafist Sunni Islam, there are specific issues that Islamic State has with Catholicism.

1) False Trinity:
According to the Qur'an, true Christianity is a Unitarian faith that rejects the claim that Jesus is the Son of God. The Christianity spread by the Catholic Church is one in which Jesus is worshiped as the Son of God, the Holy Spirit is considered a partner of God, and the Virgin Mary is venerated. As a result, Catholics (as well as Protestants, Eastern Orthodox, Oriental Orthodox, and Mormons) are all false Christians and, actually, disbelievers. Historically, most Muslims did not bother to actually compare the theology of Christianity against this rubric and most Islamic Jurists considered Catholics to be "People of the Book". However, Islamic State takes a very literalist view and if any Christian argues that Jesus is the Son of God, these Christians are disbelievers and worthy of removal or conversion.

See these relevant Qur'anic Verses, translation Sahih International:

Q: 5:116-117: And [beware the Day] when Allah will say, "O Jesus, Son of Mary, did you say to the people, 'Take me and my mother as deities besides Allah ?'" He will say, "Exalted are You! It was not for me to say that to which I have no right. If I had said it, You would have known it. You know what is within myself, and I do not know what is within Yourself. Indeed, it is You who is Knower of the unseen. I said not to them except what You commanded me - to worship Allah , my Lord and your Lord. And I was a witness over them as long as I was among them; but when You took me up, You were the Observer over them, and You are, over all things, Witness.

Q: 9:30-31: The Jews say, "Ezra is the son of Allah "; and the Christians say, "The Messiah is the son of Allah ." That is their statement from their mouths; they imitate the saying of those who disbelieved [before them]. May Allah destroy them; how are they deluded? They have taken their scholars and monks as lords besides Allah , and [also] the Messiah, the son of Mary. And they were not commanded except to worship one God; there is no deity except Him. Exalted is He above whatever they associate with Him.

2) Largest Opposition & Crusades:
The Catholic Church is the largest Non-Islamic religious group in the World and is, therefore, seen as the largest possible threat to Islamic State's desire to create a universal Islamic theocracy. Historically, the Catholic Church was also the organizer of the Crusades, which shows that the Church is willing to fight against Islamic interests. As a result, attacking the Catholic Church is considered an opening salvo in the eventual world war to recreate the Islamic Caliphate.

3) Prophecy of Constantinople and Rome:
There is a prophecy written in one of the weaker sources of Hadith called Musnad Imam Ahmad. In this prophecy, Muhammad was asked whether Rome or Constantinople would fall first. Muhammad responded that Constantinople would fall first, and it did in 1453, to the armies of Sultan Mehmet II the Conqueror. This occurred roughly 700 years after the beginning of Islam. While the validity of this prophecy in Islamic circles is disputed, Islamic State leaders believe it to be accurate and an End Times Prophecy. According to them, since it took roughly 700 years for Constantinople to fall, it will take a similar amount of time for Rome to fall, which would put Islamic victory over Rome in the 21st century. As a result, taking Rome and destroying the Catholic presence there to "Islamize" it, is considered a holy action to bring about the End Times and the universal Islamic theocracy or Caliphate.

Prophecy: "Whilst we were around the Prophet writing he was asked, ‘Which of the two cities will be opened first, Constantinople or Rome?’ He (the Prophet Muhammad) answered, ‘The city of Heraclius will be opened first!'”

Please also see this speech given by an Imam from Hamas mentioning this same prophecy.

4) Conquest of Europe:
In the minds of Islamic State leaders, it is the duty for Muslims to conquer the entire world. The area most likely to fall to Islam in the near future, in their view, is Europe. As the numbers of Muslims in Europe rapidly increase, Islamic State believes that these groups can begin to enforce aspects of the Shari'a and pave the way for integration into the Caliphate. Of course, most Europeans currently are either Atheist or Catholic, which makes these populations the natural enemies of this Islamic advance. However, Islamic State sees European Atheists as Cultural Relativists who will not oppose Islamic theocracy, so it is really only the Catholics who stand as a vanguard across the continent. Therefore, destroying the Catholic institutions should make Europe more open to conquest.

5) Relations with Jews and Interfaith:
While historically the Catholic Church is well-known for its Anti-Semitic activities, most notably the Spanish Inquisition and the support of pogroms throughout Europe, the Catholic Church has changed its tune on Jews, most notably since Vatican II in the 1960s. The last three popes, John Paul II, Benedict XVI, and Francis, have actively reached out to the Jewish community to figure out a way to proceed together as allies in common cause. Catholic leaders have also reached out to Islamic leaders to create peaceful interfaith groups.

Islamic State finds both the Catholic Church's reconciliation with the Jews and attempts at interfaith with Muslims to be atrocious conduct. In the case of the Jews, Islamic State believes the most horrible things about Jews and sees any attempt to treat them decently as seriously objectionable. (Please see this video for a compilation of Middle East Anti-Semitism, which Islamic State leaders surely believe.) Furthermore, Islamic State rejects interfaith between Muslims and any group because this would assert equality and comradery between these groups and Islamic State believes that Islam is superior to all religions. It is only when Muslims are empowered and capable of repressing others that Islamic State is proud of the situation.

Answer 2

The problem is less a problem with Catholicism than the goal of creating a Muslim or Islamic caliphate which has strict sharia law.