So here is my two cents, as an anarchocaptialist.
This article should probably be re-titled as "the Social Democratic Case against Anarchocommunism" because that is consistent with the messaging and content, and it would then be technically true (the best kind of true). However, anarchocommunism is not the only flavour of anarchism, and as such, to only discuss anarchism in terms that the communists use is illogical (composition fallacy) and a massive oversimplification of the term "anarchy".
Voluntaryists such as myself are in favour of a entirely decentralised society, one where as few as possible points of centralisation exist. We also know the value of capitalism & voluntary hierarchies as a solution to societal issues, and recognise the failures placed at capitalism's feet are largely due to government policies creating unintended market consequences.
I note that @ekklesiagora mentioned:
"Decentralized can be just as fascist as centralization. Centralization can lead to more libertarian outcomes. I mean, the centralized policing in Norway is more libertarian than the decentralized anarchic policing of South Africa."
My rebuttal to this is simple: How can a state police service (South Africa) be an example of decentralisation? What is being describe is a less free state being compared with a marginally more free state, but it is not an anarchistic policing solution, and especially not a voluntaryist one. At best this is a strawman argument, unless some evidence is provided demonstrating how South African security & justice markets are not under state control.
As for William Morris, let me use your own words against you:
"William Morris, as a democratic socialist, argued that socialism will bring about social equality and eliminate class structures, so that hierarchies and the domination of man over man will be eliminated."
And he was WRONG. Socialism did not bring social equality, did not eliminate class structures and hierarchies, and has not removed the ability to have power over others when & where it has been tried. In fact, it is logically incapable of doing so, because it requires the collective to be more important than the individuals with it, and it requires collectives are given the means of having agency (the state). The same is true for communism at its core.
Groups naturally do not have agency, because there is no single mind governing the group. Only individuals have agency, and because of this the concept of socialism, indeed any form of collectivism, is inherently flawed from a logical perspective.
I have no problem people voluntarily working together, and expending their collective effort for a common goal, or voluntarily agreeing to live as part of a democracy. Those concepts are not unique to democracy or socialism, however, and in some cases within those systems of organisation, the "voluntary" bit is optional. From experience, it is rarely taken into consideration.
Voluntary actions are inherent in capitalism, however, and capitalism has never required a state in order to work.
As for Popper, though I admire his philosophy regarding science and the scientific method, he for some reason fails to apply the same reasoning here. His arguments on exploitation ignored Hume's guillotine. A government is and will always be unable to optimally regulate markets of any kind, because it cannot know all of the inherent needs and wants of the market and all the consumers within it. Its attempts at doing so inherently are examples of the administrator's fallacy, just as the concept of democracy itself is a glorified bandwagon fallacy through and through.
RE: The Social Democratic Case Against Anarchism