Here’s what I think is the most fun argument for Anarchism, and probably (I don’t know because I haven’t tried it on anyone yet) the best in terms of convincing power, although not the best in terms of theory since it works by pointing out the bad consequences of government rather than how the idea is just deeply flaw at its core.

Here it goes. Imagine that a government makes a law. For each (good) person under its jurisdiction, there are two possibilities:
1) The person agrees with the law
2) The person disagrees with the law
In case 1, the person would have followed the law anyway, so the government changed nothing by making it.
In case 2, however, two more possibilities can play out:
2.1) The person submits to the law despite disagreeing with it
2.2) The person breaks the law and gets punished
In case 2.1, do you realize what just happened? The person did something they thought was wrong – violated their conscience – because the government told them to. That means the government made them a worse person!
Now think about what happens in case 2.2. The person bravely followed their conscience instead of doing something they thought was wrong, and as a result, the government punished them – for doing what they thought was right. If you punish a person for bravely doing what they think is right despite the threat of force, then that is when you know you are evil.
Therefore, every time a government makes a law, for each good person in the country, there is:
A 50% chance that nothing changes
A 25% chance that the government threatened them into becoming a worse person
A 25% chance that the government punished the person for their courage
Now, let’s consider this same diagram for bad people:
1) The person wouldn’t want to break the law anyway
2) The person would want to break the law
Again, in the first case there is no difference, but two possibilities can play out from the second case:
2.1) The person decides not to break the law for fear of the punishment
2.2) The person breaks the law and gets punished
Analyzing these possibilities, every time a government makes a law, for each bad person in the country, there is:
A 50% chance that nothing changes
A 25% chance that you stop the bad act itself but don’t convert the criminal OR punish them, so actual gain is slight
A 25% chance that you punish a bad person
So, in summary, every time a government makes a law, there is a 25% chance that a bad person is punished, a 25% chance that a bad act is averted, a 25% chance that a good person is punished, and a 25% chance that a good person becomes a bad person! Clearly that last one colossally outweighs everything else, so all government is evil.
And to answer an objection: no, this argument does not only apply if a significant portion of the government’s laws are not what you would call a ‘just’ law. Case 2 for the good person diagram can still play out if the law is a ‘just’ one. How? Because two good people can disagree about what is right. For example, John thinks that abortion is wrong because he thinks fetuses are people and Sally thinks that abortion is okay because she doesn’t think fetuses are people (and she hasn’t realized the other reason why abortion is wrong). Both of these people are following their conscience by practicing their differing beliefs, and if a government makes a rule either way, even if it rules correctly, one of them will either stop following their conscience or be punished for following their conscience – both unacceptable outcomes. So this argument applies even to a government that makes primarily ‘just’ laws.