There is a small kernel of interesting political philosophy at the core of this insanity. The idea that you are born into a system which you didn’t opt in to, and cannot opt out of. If you’re born in the US (or most places with a functional government), you’re born subject to several layers of government that you didn’t agree to, each of whom has all the typical government powers like a monopoly on the legitimate application of violence, and coercive taxation. You have no choice in any of that. You could try to leave, but you’ll just be subject to some other government. There’s no truly “free” land at this point in history (there is, just not the land anyone wants). This is, at the very least, interesting to consider.
The sovereign citizen mindset goes from that, straight to “I can just decide to opt out”. Usually the even more hypocritical “I can use the parts of society I want to use, but opt out of the others”. The fact is that their vision is ultimately untenable and there are good reasons why things are the way there are. There are too many humans in the areas of the earth where people actually want to live to let everything be a free-for-all. The cost and compromise of living in any valuable area this day in age is that you’re subject (without your express consent) to the government that controls the land where you were born.
The sovereign citizen just can’t handle any of this and rejects all or parts of it at their convenience. They think there are magic words they can say to a cop to make the law not apply, and all manner of other insanity.