Absurdly stupid. A complete waste of time. To paraphrase Roger Ebert, I hated hated hated hated hated this book.
In just 55 gloriously moronic pages, Spooner writes "secret band of robbers and murderers" (or something very similar) 20 times. He also uses the term "pretended" 24 times, mostly followed by "agents", sometimes by "treaty" or "ambassador", just to shake things up a bit. This is like the 19th century version of using names like Obummer or Drumpf for politicians you don't like. If you have to name call the people you're criticising, perhaps it indicates a lack of faith in your actual arguments?
Spooner clearly dislikes gov't forcing people to do things. I'm with him there. But the Consitution is perhaps the greatest achievement in world history in terms of setting up a society where people are free. Millions of people. For centuries now. But since every American didn't personally sign the Constitution, Spooner thinks it is invalid. Okay, fine. Now you have anarchy and you have no solid way to protect people's rights.
It's like publishing a book proclaiming that Magnus Carlsen is a bad chess player and showing all his mistakes, ignoring the fact that he makes less mistakes than any other player. For dogmatists, it's either perfection or nothing.
Spooner offers exactly ZERO analysis of the actual contents of the Constitution. He doesn't offer any economic or philosophic insights. Taxes bad. Government bad. Constitution bad. End of story. Repeated ad infinitum. Never mind what the taxes go to. Never mind what the Founding Fathers said or the context in which they wrote and signed the Constitution.
He doesn't offer a better alternative... or even a worse one! I hate to say it, but I think I'd probably learn more from The Communist Manifesto than this book. Marx might be misguided, but at least he offers criticisms of human nature and capitalism. He might give us some idea of the philosophy behind wanting to help others, even if his conclusions lead to evil and destructive systems.
One of the problems with anarchy is that it leaves you defenceless to coercion, war and tyranny. Nature abhors a vacuum and anarchy creates a massive power vacuum. People will try to fill that vacuum. Since you have no gov't with no authority, revolutionary groups will have no difficulty in seizing power. Then you just have to cross your fingers that these people will implement a system based on freedom.
At best, anarchy rolls the dice as to what system you'll end up with. A constitution guarantees that you'll keep the least bad system for as long as possible. In both theory and practice, it hasn't been beaten.
Spooner, like all anarchists, conflates all aspects of gov't together. Protecting freedom is a completely valid and necessary role of gov't, IMO, based on strict, universal laws, the same for everyone and above even the president/king/whatever. Gov't taking from some to give to others or exercising arbitrary power is completely different. By ignoring the difference, you let flaws in some types of system justify having no system at all! From one extreme to another.
Spooner even compares literal robbers favorably with gov't. I get his point. At least some people are open about the fact that they're hurting you. But not all gov't is like that. And robbers are hardly nice. They may well kill you even if you don't resist. They're despicable.
What would you even do after being robbed without a gov't? If you're poor, what CAN you do? At least with a gov't you can report the incident and they might catch the robber, run a trial and put them in prison. Is that really a bad thing? Is that really coercion if they're punishing coercers?
When it comes to something like murder, is it really necessary to get people to sign a document agreeing that murder is bad and that they won't do it? Respecting the freedom of others should not be a choice, but rather a compulsory requirement for anyone who wants to live in a civilised society. Yes, certain laws should be forced on everyone - the very laws which prevent people from forcing things on other people!
Spooner makes the inane point that the Constitution isn't legally bonding because people didn't agree to it. But without a Constitution, what does "legally bonding" even mean? Without laws, there's no such thing as "legitimate" vs. "illegitimate". People can form agreements and break them at any time. They can murder, steal, rape, etc., without consequence. We see that in black markets all the time - organised crime, gangs, etc. They betray each-other all the time. That's human nature without laws.
He also ignores millions of people who fled socialism to come to capitalist America. By making that choice, are they not agreeing to the Constitution, at least compared to other available systems?
Spooner even seems to criticise the US for ending slavery. Again, I get his point. If people are still forced to pay taxes, in some sense, they're still slaves. But compared to what? The US did abolish slavery while the practice continued in Africa, Asia, South America, etc. But Spooner saves his harshest criticism for one of the few countries which ended the millennia-old institution. Leftists do this as well. The US is sexist, racist and homophobic, even though women, blacks and LGBT people are freer and safer in the US than 90% of the rest of the world.
This book is dripping with Spooner's hatred for the state, regardless of what it does or whether it works compared to anything else in theory or in practice. In other words, he's irrational, emotional and repetitive. But for anarchists, he's a prophet in their religion. For those who care about reality, he's a fraction of the man Lincoln, Grant, Washington and other great leaders were. People who valued freedom and recognised the necessity of law and order as a practical means to protect that freedom.