So?
A government which can arrest neo Nazis because of what a sympathizer did, can arrest ANYONE they consider to be opponents of the Established Order.
I’m guessing you feel the same about the muslim brotherhood?
That is right, and conservatives have been called “Nazis” and even worse names. I know I have been called all kinds of things.
The US actually has a history of doing likewise: Jackson exiled Indians along the Trail of Tears; Lincoln imprisoned copperheads who opposed him without trial; Wilson imprisoned Eugene Debs and Charles Schenck for speech crimes; FDR imprisoned Japanese-Americans without trial because they had Japanese grandparents.
In each case, the Supreme Court ruled such actions were constitutional and the President went unpunished for gross violations of natural rights. In fact, high school history teachers throughout the Land regard these four among the greatest of US presidents, and their images decorate US coin and currency.
If the President wishes to harass, imprison, or even murder somebody, he can, provided either that the somebody is sufficiently unpopular or that he can keep it secret. Contrary to the civics lessons taught in junior high school, that is the way government really works.