Except the racial purity argument seems to be moot with Europe's agressive policies of MidEast resettlement. You would have to explain how they plan to clean up the mess for their end game..
There has to be some other motive.
I'll go with the "family purity/genetics" as a side concern for them specifically.
They have been working to destroy family, morals (perhaps religion as part of those two) and culture for decades along with the concept of national identity. That would seem to be a first step in their plan.
The Muslim issue is still a puzzle with regards to this, however, because they (also Hispanics in the US) seem to be strong in all the areas (family, religion, culture) that the elite have been destroying in the West. It leaves us trying to figure the end game because they look to be creating a bigger mess for themselves if immigrants become dominant in anglo-Christian countries.