Lex Anteinternet: Islamic Violence, Islamic Silence and Western Rela...:
For the first time, I've heard a really good explanation, but a noted religion writer, on the topic of this type of violence and Islam.
Of note, according to this author, who seemed very well informed indeed, such violence is in fact not sanctioned by Islam, even if Islam's history and texts have some violent aspects. A partial reason is that there's no authority that has authorized it, which can authorize it. Indeed, there would appear to be no authority which can in fact authorize it.
Additionally, it appears that the violence has in fact turned off a large segment of the Islamic population everywhere, to such an extent in fact that the religion is loosing a significant number of adherents in some areas, including Iran, where those abandoning the faith are either completely abandoning any faith, or are converting to Christianity.