Why is it considered racist for Europeans to want to limit Black/MusIim immigration?

Blacks and Muslims come over in hordes and have 10 kids each. Pretty soon they're going to outnumber native, white Europeans in our OWN countries. So why is it racist to want to keep these people out (or at least make sure not too many of them come in)?
Update: @Sydney: That's true, most most muslims are either African or Asian. The point is that they're not native, white Europeans.
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