They think the law is magic, and that lawyers and the police are like the fae folk.

All of their rules are written down, and if you can just find the right magic words you can free yourself from the system. Cops can only arrest you if you consent, which requires you to say the special words that tell them you don't accept their authority: you're a sovereign citizen, not a US corporate citizen, because the police only have authority over people who agree to be bound by the rules that bind US citizens.
And the courts only have authority if you accept it, and you don't have to if you recognize that that the flag they're flying openly declares this court to be under a different jurisdiction, because only maritime flags have a fringe, and so the court isn't actually a US court but a maritime court, so you can petition for a change of jurisdiction to a different court, but you have to be careful not to accept any of their authority or accidentally bind yourself to taking responsibility for the secret shell company that the US created for you that is your name spelled in ALL CAPS, otherwise you're bound by their rules.

It's entirely bonkers, and based on layers of not understanding the law, magical thinking, conspiratorial thinking, and being taken in by a scam.