Let me reverse your question:
There are a lot of American-owned websites that today promote Nazis, holocaust denial, a state seceding from the U.S., etc.
Should the federal government ban those websites?
I don’t believe we are at present at war with Nazis or holocaust deniers. Even secessionists are presently expressing political opinions, not engaging in armed assault on US forces.
In 1861 and again in 1864 CSA armed forces actively engaged in war against the USA were within 10 miles of the White House.