I expect that -if you make a close study of history-, you'll find that "[America's greatest strength is its ability to assimilate people and ideas into something greater than the sum of its parts as] long as [those people] are white and [those people and ideas are] christian..." is a statement that isn't supported by the facts.

Xenophobia and racism was and is real, yes. But, -culturally and ideologically- the US has been and remains substantially less homogenous and substantially more willing to accept immigrants into its borders than many other countries.