The cafeteria type Christian is a recent phenomena. Even in the World Wars the Church held much more power and influence than they have today. Without invoking Goodwin's Law. A big reason for the ease at which Hitler was able to oppress the Jewish people was the sentiment that "the Jews murdered Jesus" and this position was held by the Roman Catholic faith up until the 1960's. The Christian religion is not a toothless organisation with no influence but going back further in history, the influence that it exerted to its followers and the nasty zealous conviction of its tenets and its leaders was the cause of a lot of intolerance and violence in its name. It did not mean that every follower of Christianity was a zealous, hateful righteous bigot BUT it DID mean that they were not the loud voices or prepare to stand up against Christianity.
Islam is the same thing now. I do not know if it is more moderate or more fanatical but it is in the same ballpark of what Christianity was a few centuries ago. I do believe that most Muslims are not radicalised nor bad people. In fact I have spoken to fundamental Muslims who can shore up their beliefs nicely and in a way that makes them decent and law abiding and good people to know. I have spoken to Moderate Muslims who are like Cultural Christians or Cultural Jewish People.
The problem is that not only do we not know the number but any statistic you give to me is likely to look scary when you talk of mass immigration in the millions. Let's say 1 000 000 Muslims immigrate and of them 50% strongly reject the kind of values that their host country has and most of that 50% refuse to integrate. It does not then matter the number of them that are moderate. You can tell me 500 000 immigrants were easy going and compliant. That would not be my focus. You could say only 10% are real trouble. But that doesn't bother me either. What would bother me more is that that 10% was supported by people who are happy to look the other way when they are talking 13 year old brides, when they are involved in gang rape, when they sprout Western intolerance in Western countries in mosques, and the want for their own laws (Sharia) to govern them in another country.
That would bother shit out of me. When you are talking numbers of 1 000 000 people then talking of 50% or even 1% of collective zealots infiltrating a new host culture with a lot of hate and great network, then this is a problem. In addition the ability for large amount of Muslims who BECAUSE of their religion and common interest and culture will not necessarily do wrong by the new culture but will look the other way and forgive it when others do.
It don't necessarily mean everything should stop or the baby should be thrown out with the bathwater BUT there needs to be a critical examination on this issue without the fear of doing so to avoid being called a racist or an islamophobe.