Others also do it?

If anybody claims that Islamic terror is doctrinally justified (which is a fact), they are confronted with the fallacious argument that other religions are no better. There are portions in the scriptures of Christianity and Hinduism that are not exactly in consonance with the ideas and ideals of the Enlightenment. Since all religions have preached violence—and their adherents have slaughtered non-believers, the blasphemous, and heretics—Islam should not be singled out for doing so. QED.
The fallacy lies essentially in blurring the timeline, misinterpreting the impact of various theologies, and leveling religions. It is true that the scriptures of other religions also preach violence. In the Bible, Lord sanctions the enslaving of strangers or heathens; He also exhorts the faithful to kill anyone who worships a different god .
Similarly, in a famous verse, the sacred Hindu epic, Ramacharitamanas, says, “A drum, a rustic, a Shudra (an outcaste), a beast and a woman—all these deserve to be beaten. Similarly, Manusmriti, the book by the preeminent lawgiver, Manu, makes derogatory remarks about women and Shudras. In short, it is not only Islamic scriptures which preach violence and intensify prejudice; the religious texts of other faiths are no better in this regard.
For centuries, Hindu texts have not only molded legislation and social mores in India—in the same fashion that Christian dogma and prejudice have been the cause of witch-hunts and atrocities on Jews and heretics. In India, religious bias still sometimes results into unspeakable atrocities.
But the point is that today Hindus and Christians are not doing the terrible things that their forebears did in the medieval period. Nor are they demanding that the polity and society should be reorganized according to their religious texts. In the case of Islam, however, such demands are forcefully made—and accepted partially or fully. A large number of Muslims, including many educated and apparently Westernized Muslims, want Shariat to be the fount of jurisprudence.
Worse, liberals compare the atrocities perpetrated by the Hindus and Christians in the medieval period with jihadi terror in the 21st century, and try to show that there is nothing exceptional about such terror.
The fact is that Islamic terror in this day and age is exceptional: while the adherents of other faiths have discarded the distasteful elements of their religions, Muslims refuse to follow suit. A vast majority of them believes that the Koran is the Word of Allah and, therefore, is unalterable. Exegesis has found little space in Islamic theology—at least, till date. Other religions like Hinduism and Christianity have evolved over the centuries. The way Hinduism was practiced in the 14th century—myriad rituals, degradation of Shudras, subjugation of women, elaborate caste rules, rigid customs—is not how it is done today. Ditto with Christianity. It is not that nothing has changed in the Muslim world but the change has come in spite of, not because of, Islam.
Muslim scholars and many non-Muslim experts on Islam do not deny the lack of evolution in the Islamic world, but they refuse to see anything wrong with Islam. For instance, Mohamed Charfi—a Professor of Law in Tunis, Minister for Education (1989-94), a great reformist intellectual who was sentenced to two years' imprisonment—says, “Islam is no less capable of evolution than Christianity or Judaism. But whereas, over the past few centuries, Europeans have undergone profound technological, economic, cultural and political changes, often amid considerable suffering and with major ebbs and flows, the Muslim peoples have fallen greatly behind in all spheres. This is not a fate to which they are doomed for ever; it is possible for them to close the gap.”
The unwillingness to look beyond the “technological, economic, cultural and political” factors, the reluctance to examine Islamic theology is at the root of problem. Hinduism, Christianity, and other religions have been subjected to thorough scholarly scrutiny. The loathsome practice of female feticide is (rightly) attributed to certain Hindu beliefs. But when it comes to Islam… well, we have to be careful.
Then there is the issue of religions leveling. Well-known Islamic scholar Karen Armstrong wrote, “Every fundamentalist movement I’ve studied in Judaism, Christianity and Islam is convinced at some gut, visceral level that secular liberal society wants to wipe out religion.”
Notice the dangerous syllogism. All fundamentalist movements are illiberal; Islamic fundamentalism is also illiberal; ergo, it is no worse than other fundamentalist movements. The danger lies in confusing the magnitudes: Hindu and Christian fundamentalists might have been involved a few, sporadic violent incidents, but neither the scale and scope has been as vast as evident in the case of jihadis nor the level of organization and commitment as exhibited by al-Qaeda.
The entire Muslim and liberal enterprise is oriented around the unexamined axiom that the violence by jihadis is not about Islam. But, as Salman Rushdie said in a famous post-9/11 article, this is about Islam.