It's also a well known fact. All you have to do is look at the demographic changes in Western countries.
Wanting white culture to survive still doesn't make one a white supremacist. I even want Japanese culture to survive. Does this make me a Japanese supremacist?
You change the original point. Professing "white culture" is under threat and that other cultures should survive someplace else does indeed make you a white supremacist.
The U.S. was multi-cultural from the start, even if some cultures (natives or blacks) wanted nothing to do with it. This is what made it later stand out and attract people all over the world. You can't re-neg it without turning into a genocidal shithole.
What do you mean by this?
Are you saying that American culture is "white" culture? If so, then you might want to do some self-reflection.
It is fair to say that most organised attempts to advocate for 'White Culture' -such as White Pride events and a staggering proportion of 'European Students Associations' etc are explicitly racist in practice. This by itself should be concerning enough to lead observers to scrutinise very carefully organisations or publications devoted to securing 'White Culture'.
White people are too ambigously defined a group to have one common culture. Hence the term is nonsense.
Is this statement morally equivalent? Why or why not?
White people are too diverse a group to have one single culture. I am white and not from the U.S. Based on these facts people cannot guess what my values are, what my traditions are, whether people of my ethnicity were ever opressed or were the opressors, or even what language I speak, or what religion I have. Hence the term "white culture" does not make sense.
Cultural globalisation merges all cultures into one common. Small (or less vocal) cultures get less representation in the global culture, while large ones get incorporated more wholesale. Cultural diversity in contrast try to keep cultures distinctive, while also trying to dodge cultural tensions. White supremacists generally require that cultures stay distinctive, but they don't care to decrease cultural tensions. That doesn't seems to fit well for either side, and makes attempts to do so to look as political attempt of associating white supremacists with criticism to multiculturalism.
'White culture is under threat' is a core belief of white supremacists.