The basic ethical ideal of a perfect state is that perfect justice is always perfectly done, but how do we pay for it?
People are not always rational. Miscarriages of justice will happen. Getting the just restitution (and costs) due actually paid by those found liable in civil or criminal cases is not always possible. People want what they want but they often don't want to pay for it until and unless they actually need it themselves.
A person who's never been in trouble with the law or has never been offended against often doesn't put a lot of value (and value judgements are always subjective) into the ongoing operational costs of a justice system. On the other hand, a person who has been sued or charged with a crime, rightly or wrongly, or has been offended against, suddenly puts a lot of value into a justice system that will give them the outcome they want, whether actually just or not.
That's simply human nature.
Accepting all this reality means that there is no perfectly just system possible. It then becomes a matter or looking at the various possibilities and finding the trade-offs that come closest to it.
Voluntaryism is great, but is rarely sufficient.
The general benefits of a justice system are amorphous. They often can't be pinned down to what person gets what value or even what that value is.
A person who owes, whether to the justice system for costs or to the person to whom reparations are due, may simply be unable to ever pay them.
And all of this doesn't even start to consider the ongoing costs of a military capable of defending a given geographical area in today's world.
So it may be that some sort of tax is the most just feasible way of distributing those costs.
Then the question becomes what kind of tax.
A head tax would be the most just, based on the assumption that everyone's life is of equal value. But the reality is that many people would be simply unable to pay an equal portion of all the costs associated with even a minimalist government.
So we need a measurable characteristic that will, as justly as possible, also take into account a person's ability to pay. Monetary value of something, especially when we're considering monetary financing of a system, is the next best way.
But how do we determine an objective value for something in and of itself? We can't, since value is subjective. The closest we can come is the value that two people place on something at the time when it is actually transferred from one person to another.
That brings us down to another two choices. The tax can be assessed on the sale itself or, for durable goods or land, an ongoing assessment.
Both of them have significant problems. For a sales tax, who collects it? How do you enforce it? For durable goods or land, what do you do about the fact that some assets depreciate in value over time and other appreciate. Who decides the value at any given time? And, once again, how do you enforce it?
At this point I've got more questions than answers. Some sort of compromise among all the possibilities has to be reached. Some sort of answers have to be decided upon. But I don't feel competent to declare what those compromises and answers *should* be.