Nazism is illegal in Germany, it is not a crime in America. Neither is communism, anarchism, or Islamofascism although all three preach sedition.
There have been periods in American history when there have been laws against sedition but they are repealed when the threat has passed.
Interesting little defense mechanism in Islam; when a nation prohibits the exercise of the faith, all Imam agree that is the clear sign that physical holy war/jihad may be waged against a country.
Actually, the threat had not passed when the Alien and Sedition Acts expired. Luckily for our country, Jefferson had been elected, and was able to successful lead the country forward (as did Madison after him) without them.