I'd like to throw my two cents in, without going too deep into the debate:
I live in Berlin, Germany, and I know quite a few people with immigration background from Muslim countries (see? I am even hesitant saying "Muslims", because according to my experience, most of them are not even religious Muslims). It's true there are some problems with this group of people. Especially young guys from Turkish families often don't know how to behave properly, they seem very macho, often display an authoritarian attitude, they have an awkward attitude towards women, they are overrepresented in the crime rate of that age group.
But according to my impression, this has nothing at all to do with Islam. On the contrary. Those who actually care about their Muslim religion are usually better integrated, they restrain from crime, they respect women better, they don't display this ugly "young male teen mob" mentality. But of course the really Muslim people among them are sometimes awkward too -- very conservative views on gender roles, homophobia and so on, much like hardcore Christians. But hey, we're a free country, so as long as you respect the law, you're free to believe what you want. Actual support of terrorism really is only a mere fringe phenomenon, even among those few immigrants who actually care about Islam.
If you ask me, the problems we're having with young 2nd generation Turkish immigrants have nothing to do with Islam, but mostly with social status and backwards *tradition* (as opposed to religion) -- and bad education. Their parents are usually from very backwards East Anatolian regions, sometimes almost illiterate, hardly any education. Accordingly, their style of education is very authoritarian on one side, but on the other side, they give their sons too much leeway (their daughters are usually the nicest people on this planet). Religion does not even play an important role within their families, but backwards gender roles, family "values" and antique ideas of honor (you sometimes find this among backwards Christians in south Italy too). Of course the sons growing up in these families experience a clash of culture when being confronted with lenient, anti-authoritarian and individualist values in kindergartens, schools and sports clubs mostly frequented by natives. Some manage to make this tightrope walk, but others do not and then are trapped between cultures, are prone to crime and awkward behavior.
Why do people believe this has anything to do with Islam? I really have no idea, because it is more than obvious that it does not.
The rampant aggressive islamophobia among natives, on the other side, really worries me. Maybe that's because I don't understand it. Most of their ideas could not hold any scrutiny at all, if the islamophobes took the effort talking with actual Muslims only once. Usually, it's people who have some obscure fear, they apparently feel horribly threatened by anything that's alien and not culturally and racially pure, and they paint all immigrants from Muslim countries alike with such a broad brush that the resulting caricature seems ridiculous. I feel pity for them, because they must have a really ****ed up, pathetic life, when they are so horrible scared all the time. But what scared them so much, what went wrong? Did a Turkish yob mock them in a subway? Did a Turkish Döner Kebap seller cheat them for change? Big deal, happened to me too. But why, for Christ's sake, can't they just relax a little about it? **** happens.
On top of this deep fear, there apparently is much rage and hate, which worries me. All I get from the islamophobes is that they hate immigrants from Muslim countries. Constructive ideas about what to do, how to proceed with them? Never. Just as vague and undefined as their fear is, so is their hate. They just somehow want these aliens to vanish -- their mere existence bothers them, much more than their behavior. No clear, rational definition, just vague fear and hate. That worries me, because I feel they might even support a "final solution to the Muslim question", if the right demagogue proposed it. But maybe that's a stretch, I don't know. At any rate, I have never heard anything constructive at all from islamophobes. Not even a single time.
At any rate, islamophobia is objectively a much bigger threat to a free open society, a much bigger threat to democracy and freedom, than radical islamism is: Islamophobic parties on a platform of fear, hate and ostracism make up to 20% in European elections. Muslim political parties which might be a threat? As far as I know, such a party does not even exist, nowhere in Western Europe. Now if an islamist party with the goal of establishing a califate (a demand, which I believe, not even 5% of the immigrants in Germany from Muslim countries would support) was formed, and won considerable political influence, I might agree that there was a problem. But such a party is decades away of even being formed. Why all this paranoid hysteria? What's wrong with people?
And yeah, we should do a better job to address the problems with immigrant yobs and deranged teenagers. If their families can't give them a proper education, maybe our society should find ways to address this deficit. It's not a good thing when too much of them run around pestering women with vulgar slogans, selling drugs or beating up each other. But I really don't see that Islam plays any significant role in this.