My case for anarchy is based on moral evidence. The issue is much simpler than people think. It is almost always wrong to use violence or the threat of it against another person. No one - no one worth arguing with, anyway - seriously disputes that. Yes, it can be justified under some circumstances - when one is in immediate danger or someone else is - but not otherwise. (There's of course room for a bit of debate over when one can legitimately use violence against another, but not much....every reaonable person is going to agree that the boundaries are pretty tight, even if there's no consensus on precisely where they lie).
It is also obvious that having more power than someone else doesn't make one more entitled to use violence against another. I am much stronger than Susan - does that mean I can use violence against her? No, obviously not. Might does not make right.
From those simple and uncontroversial moral axioms, we can derive the verdict that no one in power is entitled to use their power - their ability to use violence and the threat of it - against others in ways that we ourselves would not be entitled to.
And in one fell swoop, that reveals the injustice of the vast bulk of what the government does.
But that leaves those exceptions - the cases where we are entitled to use violence against another, such as self-defence or the defence of another's life. If someone is attacking you, I am entitled to defend you against that attack, with violence if necessary. So, aren't those in power entitled to do the same?
Yes, of course, for that is just an application of the same basic 'might does not make right' principle. If I am entitled to protect you from attack, then so too is someone else.
The problem is that though I am entitled to protect you from attack, I am not entitled subsequently extract some payment from you for having done so and use violence against you if you fail to pay. And I am certainly not morally permitted to announce that I will defend you from attacks (whether you wish me to or not) and then insist you start paying me for that service (and threaten you with violence if you do not pay me).
I take that to be obvious. Yet that is what the government does. So, if we imagine - for the sake of illustration - that government to be a person, then it is behaving immorally, for though some of what it undertakes to do it is perfectly entitled to do - as is any person - its insistence that we pay for its services or face violent consequences is clearly unjust.
And now we have arrived at anarchy. Nothing the government does is just. For if the government sticks only to interfering in our lives in ways that we would be entitled to interfere with each other, and sticks as well to inviting payment for such justified interference rather than extracting it with menaces, then it ceases to be a government at all and is just a bunch of individuals touting for business.