Culture and ethnicity should not be used interchangeably. A society can lose its culture and have its ethnicity remain largely intact, while it would be exceptionally difficult to lose your ethnicity and have your culture remain intact.

Likewise, you can absolutely believe that there are things that make your culture superior to other cultures without being a racist. You can absolutely believe that certain cultures are evil, such as those that engage in human sacrifice, and should therefore be wiped out. However, once you believe that your ethnicity is superior to all other races, such that those other races should rightly be subject to yours or else be wiped out, simply because of their biology, then you have crossed the line into racism.

It's muddy waters because ethnicity and culture often so closely overlap one another, but they are not the same and should not be treated that way. A person coming out of a morally bankrupt culture may align himself with a superior culture while his ethnicity remains the same. Ethnicity we inherit by blood, but culture we inherit by being steeped in it from birth. One we may renounce to our good or ill, based on what we replace it with, while the other we have no choice in whatsoever.

This is also why I believe the idea of preserving the United States as both white and Christian is misguided, though not necessarily racist. What we should be trying to preserve is the Western brand of Christian culture. If other ethnicities find that culture attractive and wish to renounce their own in order to adopt it, more power to them! It's when folks want to eradicate that culture, regardless of their ethnicity, that we should have a problem with it.