"...we should be eternally vigilant against attempts to check the expression of opinions that we loathe and believe to be fraught with death."
--Supreme Court Justice Oliver Wendell Holmes, Jr., dissenting opinion in Abrams v. United States, 250 U.S. 616 (1919)
So, who's opinion can't be expressed?
I mean, beside those of the people the Nazis attacked.
Monuments to white supremacy are not free speech. You are still quite free to express any white supremacist beliefs, and the presence or lack of a statue has no effect on that.