I take a slight step to the side from Why I am not a Muslim to introduce this piece by Ibn Warraq (reproduced in full, with a link at the end)
It is quite common to hear two arguments from Muslims and apologists of Islam, the language argument, and that old standby of crooked, lying politicians, “you have quoted out of context.”
Let us look at the language argument first. You are asked aggressively, ‘do you know Arabic?’ Then you are told triumphantly, ‘You have to read it in the original Arabic to understand it fully’. Christians, even Western freethinkers and atheists are usually reduced to sullen silence with these Muslim tactics; they indeed become rather coy and self-defensive when it comes to criticism of Islam; they feebly complain “who am I to criticise Islam? I do not know any Arabic.” And yet freethinkers are quite happy to criticise Christianity. How many Western freethinkers and atheists know Hebrew? How many even know what the language of Esra chapter 4 verses 6-8 is? Or in what language the New Testament was written?
Of course, Muslims are also free in their criticism of the Bible and Christianity without knowing a word of Hebrew, Aramaic or Greek.
You do not need to know Arabic to criticise Islam or the Koran. Dr. Paul Kurtz, founder of the Center for Inquiry, and Prometheus Books, does not know Arabic but he did a great job on Islam in his book The Transcendental Temptation . You only need a critical sense, critical thought and skepticism. Second, there are translations of the Koran by Muslims themselves, so Muslims cannot claim that there has been deliberate tampering of the text by infidel translators. Third, the majority of Muslims are not Arabs, and are not Arabic speakers. So a majority of Muslims also have to rely on translations. Finally, the language of the Koran is some form of Classical Arabic  which is substantially different from the spoken Arabic of today, so even Muslim Arabs have to rely on translations to understand their holy text. Arabic is a Semitic language related to Hebrew and Aramaic, and is no easier but also no more difficult to translate than any other language. Of course, there are all sorts of difficulties with the language of the Koran, but these difficulties have been recognized by Muslim scholars themselves. The Koran is indeed a rather opaque text but it is opaque to everyone. Even Muslim scholars do not understand a fifth of it.
Let us now turn to “you have quoted out of context”. This could mean two things: first, the historical context to which the various verses refer, or second, the textual context, the actual place in a particular chapter that the verse quoted comes from. The historical context argument is not available, in fact, to Muslims, since the Koran is the eternal word of God and true and valid for always. Thus for Muslims themselves there is no historical context. Of course, non-Muslims can legitimately and do avail themselves of the historical or cultural context to argue, for instance, that Islamic culture as a whole is anti-woman. Muslims did contradict themselves when they introduced the notion of abrogation, when a historically earlier verse was cancelled by a later one. This idea of abrogation was concocted to deal with the many contradictions in the Koran. What is more, it certainly backfires for those liberal Muslims who wish to give a moderate interpretation to the Koran since all the verses advocating tolerance (there are some but not many) have been abrogated by the later verses of the sword.