The ideas of voluntaryism are sometimes criticized as utopian fantasy because “it just won’t work”. These people come up with difficult questions and hard problems that a voluntary society would face, and because the person they are asking doesn’t have the answers (or no one does), they assume that the status quo of statism is the only workable system simply because it actually exists. The problem with this kind of thinking is that it will agree that voluntaryism may be the only moral society, meaning that it agrees that it is the only system that should exist, it just denies that voluntaryism can exist or that it will function well, therefore it should not exist and not be the libertarian end-goal. It is pretty obvious that this line of thought is contradictory because it believes that a voluntary society should both exist and not exist at the same time, and it is a non-sequitor that because you cannot comprehend a voluntary society existing in reality that it should not exist.
So regardless if you can’t imagine a voluntary way of solving a technical problem, it doesn’t magically justify aggression. Minarchists in particular are guilty of committing this fallacy. The only consistent position to take is the anarchist, or voluntaryist, position. It is not possible to know in advance how people will live and thrive without initiating force against each other, but it is possible to speculate on the likely free market methods for provision of things like defense, justice, roads, and protection. This has been the subject of many excellent books, some of which I will do here (all of these are free on Mises.org):