There's no 'white' culture, there is modern North American culture and it's not something that belongs to a particular complexion. It's norms and traditions. These aren't remotely under threat of extinction from 'race mixing.'

The things that are under threat are the contemporary cultural values of openness and acceptance of other cultures/relgions/traits. These are truly valuable, positive aspects that stand out in contemporary American and European societies, and these are the things that are legitimately under threat, ironically, by those who attempt to normalize racism and xenophobia.