The Porkies Register
In discussing such a serious and emotionally-charged topic as Islamic extremism, it cannot be overemphasised how important facts are. Many Islam-critics seem to be unable to understand this, and take the attitude that there are so many facts to condemn Islam, that the lies don't fundamentally make any difference to the "truth" of Islam. Of course we get the usual indulgences of logical fallacies to explain them away, especially the tried and trusted "its up to you to disprove its not a lie" [1][2]. Some even go so far as to hold Islam responsible for the perpetuation of lies against Islam [3].
It shouldn't need explaining why accurately citing facts in a discussion is in and of itself important. Those who are willing to resort to misinformation and outright lies, either through ignorance or deliberate deceit, by default have a compromised argument - regardless of how little difference those mistruths may seem to make on the overall argument. Apart from anything else, it hurts the reputation of the people making those arguments, and just like the boy who cried wolf, when accurate facts to incriminate Islam are presented by the same side, the claim will naturally be viewed with suspicion.
Misrepresenting the Quran: Deception_of_Non-Muslims#Lying_about_the_Quran
Misrepresenting the Bible: Deception_of_Non-Muslims#Lying_about_other_religions
Misrepresenting the Torah: Muslims_Promote_Genocide#Jewish_Law
Justifying and misrepresenting Muhammad's genocide of Jews: Muslims_Promote_Genocide