So, let's first establish that these are individuals and that while for some of the individuals targeted your claims hold true there are many others that did successfully integrate. For the rest I'll ignore those but they exist and their numbers are vast, much larger than the numbers of those that failed to integrate but since they're not 'part of the problem' I'll pretend we're not talking about them (though they should be talked about because they apparently hold the key to at least a part of the solution).
You're forgetting a few not-so-juicy details. Most of these people that failed to integrate carry local passports and to the law they are just as French (or Dutch, or German or whatever) as the rest of the people living there.
As a rule all these countries practice freedom of religion so whatever the effect the immigrating (grand)parents had on the statistics of decades past the problem is the effects today. And you can't attack anybody on grounds of religion without opening up the traditional make-up of the country as well so that's right out because it would make a great many people in various power structures extremely nervous.
The failure then is to fail to fully integrate these people, part of the failure is theirs, part of the failure is ours.
The fact that the younger generation (and definitely not all of them!) are unable to get work, unable to find meaning in life and unable to get ahead no matter how hard they try creates a level of frustration that I can only imagine, but which broke through partially in the riots in France a couple of years ago.
As far as the 'double digits' are concerned, right now an ultra-rightwing party holds > 25% of the vote in NL, that doesn't make all the Dutch racists any more than 30% of the Muslims agreeing with some or all of the terrorist activities makes all of the Muslims supporters of terrorism.
It's each and every person as an individual that matters.
And if a person specifically supports these acts then you can go after them with whatever tools are available but until then there is no reason to act in a generalizing manner. That only makes the problem (potentially much) worse.
