Though flawed, Bret Stephens' In Defense of Christendom sounds an alarm that ought not be ignored:
Could Europe’s liberal political traditions, its religious and cultural heritage, long survive a massive influx of Muslim immigrants, in the order of tens of millions of people? No. Not given Europe’s frequently unhappy experience with much of its Muslim population. Not when you have immigrant groups that resist assimilation and host countries that make only tentative civic demands.
Assimilation is key. Are the Muslim immigrants willing to assimilate? Are they willing to adopt the values and culture of successful societies that promote human flourishing? Or is it their intention to enjoy the benefits of successful societies while retaining the values and culture that account for the unsuccess of the societies from which they flee?