Western civilization/culture has always been multi-ethnic, and that's not the cause of major strife, just as within the Islamic world. To remain desirable, the West should welcome from anywhere anyone who can make the West a better place, as it has done for centuries.

The West rather needs a better way to get rid of the hostile invaders who want to burn the place down or fundamentally eradicate Western values. Surrendering culture in the name of inclusiveness is just a flagrant own-goal, and certain Western societies have themselves primarily to blame.