Essentialism is a fairly universal tendency of seeing things as have defining qualities. Without some kind of essentialism it would be hard to distinguish one sort of thing from another. Science, for example, has its essentialists (indeed, the periodic table is based on essences), and no doubt the fans of football, cricket and hockey, chess, monopoly, and other games, have what they consider to be essential properties of their favourite games. Your claim, therefore, that “essentialism is one of the cognitive biases that both underlies and is encouraged by religious thinking” is really quite misleading. Wittgenstein, as you are no doubt aware, was opposed to this sort of essentialism, by pointing out that the meaning of a word is constituted by its use, and he used the example of games to make his point. There is no one essential feature of all games, he suggested, that determines the use of the word ‘game’. I think he was probably wrong. Games are almost always characterised by quite contingent rules and limitations, so that playing a game is only possible if there are some things that do not constitute “moves” in the game. Otherwise, we have rather untstructured play, instead of a game.
So, of course, when we are talking about Islam or Christianity or Buddhism, or any other religion, we are going to home in on some of a religion’s most characteristic features. You want to let Islam off the hook, by suggesting that in picking out features of Islam that seem to characterise it (in some sense universally), we are being both arrogant (in claiming to speak thus about anything of which we are not believing members), and xenophobic (in this case Islamophobic).
But Islam does have fairly universal features. Not that every Muslim engages universally in these features, but in that historically, and in terms of its own doctrines, the practice of Islam has been so characterised. And violence, even aggressive warfare against non-believers, has been one of those features. Not only is this an observational datum, this feature of Islam is deeply embedded in its doctrinal tradition as well. It is present in all the fundamental Islamic texts, including the Quran, the Hadith, the Sira, the Sharia, etc., which, altogether is called the Sunnah.
Jihad, as offensive war against non-believers, is a duty of all Muslims to support, even though, as the Quran says, they may find it distasteful. And it is their duty to engage in it until the whole world is subject to Allah and his holy laws. Ayaan Hirsi Ali, in her most recent book, Heretic, speaks of this sort of Islam as Medinan. The “revelations” to Muhammad in Mecca are altogether more peaceful, but Muhammad’s stay in Medina produced very different “revelations”, in which a more warrior spirit prevailed, in which violence against unbelievers, and the murder of those who spoke critically of Muhammad became normative for the followers of Muhammad. Hirsi Ali thinks that Islam could be reformed by returning to the Meccan variety of Islam. I doubt this is possible, but it is not simply Islamophobia to point out that Islam has traditionally been spread by means of the sword. And being an honour-shame culture, Islam has almost always opposed anyone who calumniates Muhammad in this most savage and brutal ways (in order to restore its honour), even though the religion he devised was really nothing more than a protection racket, swelled in numbers by conquest, and the forcible conversion of people holding other beliefs. Europe was only spared Muslim occupation in the nick of time, just before the development of science and democracy in the West. Islam made incursions from both the West, where it was defeated (at the Battle of Poitiers or Tours, in 732), and from the East, where it was defeated at the gates of Vienna in 1683, although it overran Greece and the Balkan states.
For a time Muslims dominated Sicily, and much of southern Italy, sacking Rome at least once. Greece was subject to Islamic conquest and occupation. The Greek war of independence began in 1821, and with the intervention of the Western powers, Greece became an independent state by 1832. Lord Byron (the poet) played a part in the revolt against the Ottomans (and the Egyptians, who came to the rescue of Ottoman rule) and is still recognised as a hero in Greece where a day is set aside in his honour.
So let’s not pretend that Islam is not a warlike force, and that it did not engage, as it still does, in violence against non-believers and apostates in its struggle to dominate the world. This is at least one of the essential aspects of Islam, which makes it a danger to everyone who does not share the Muslim faith. Islam has already made significant inroads into Western nations and their polity. Indeed, suppression of free speech (such as you endorse yourself, Mr Walker) is well on the way to becoming established in Western democracies.