Caldwell's arguments are certainly based on fallacious and racist premises. However, he is not wrong that increasing Islamic influence is to be viewed with alarm. My context for stating this is that any increase in religious influence at the societal level is alarming.
In its best form, spirituality is an intense personal experience, and houses of religious pursuit (churches, mosques, etc.) serve as places where one can get instruction on how to directly effect contact with the spiritual being in which one believes. Treating one's religion as a public matter is destructive to separation of church and state, a separation that I see as one of the greatest needs in modern society. People like Rod Parsley, who began the "Patriot Pastor" movement, scare the heck out of me. They don't understand that theocracies (whether brazen or subtle) are abusive regimes, because there is no way to challenge the power structure since the authority in such governments is God-given.
Regarding Ms. Lalami's criticisms of Caldwell, she is spot-on about the spotty scholarship, which is detestable. However, she has likely not plumbed the depths of what truly drives the marginalized groups in Europe. Without having visited Europe, it is hard to speculate exactly what is occurring within the crania of second-class citizens there. Still, heaven forbid that such difficulty of accuracy should prevent me from trying.
I think that the majority of Muslims in Europe are just trying to get by. Unfortunately, like minorities in the US, by birth European Muslims are in a group that is politicized (whether they like it or not) and they must either behave exceptionally or they will "fall between the cracks" in society. I think that having so little room for error tends to make people open to radicalization, and so a few of these people become open to the idea that there is a war on between Islam and Western culture. This notion is reinforced by the similar (but different in crucial aspects) fact that there actually is a war on within Western culture between religion and secularism. Anyway, the few who become radicalized then are open to committing criminal acts in the name of jihad.
I think that a significant part of the concern of Europeans toward Muslims is not simple racism--it is a concern that people are living among them who are not invested in their society, for reasons of class, culture and religion. When I see a hijab or burka, I react not because I detest Muslims but because I view the veiling of women as a symbol of their (unfortunately internalized) control by traditional patriarchal culture and religious dogma. Choosing to veil in public in a society where the significant majority of women do not do so is a political act (whether one intends it to be so or not), because it shows one's disregard for the values toward which Europe has been trending in the recent past. Thus, the suspicion of "white" (for lack of a better term) Europeans towards Muslims is understandable, while not entirely justifiable. White Europeans must do the internal psychological work to maintain the validity of their concerns. They must reject people like Le Pen and Caldwell, and they must look within themselves to determine that what they are feeling is a relatively pure desire to preserve secularism, and not a convenient cover for racism.