The only strange thing about this is that the Sith aren't just leading armies openly, but manipulating events in secret. Dooku admitted to being a Sith, and that there is another Sith controlling the Republic. The Jedi and Republic know that the Sith are an existential threat to their continued existence. The Republic has learned through billions of slaughtered civilians that the Sith are incurably evil in the purest sense of being dedicated to power acquisition at any cost. The Star Wars galaxy is a horribly dangerous place, and the sith are one of the most successful dangerous groups in it. They have led multiple empires in the past with the Express purpose of destroying the Republic and literally bending the galaxy to their will. Yes, being a Sith is a crime in the Republic.
