The point is that anarchism historically has not succeeded and cannot succeed in the real world that we actually live in today, in the face of monopoly capitalist/imperialist states that will do everything in their power to plunder the resources of all other states.

Michael Parenti, Blackshirts and Reds:

But a real socialism, it is argued, would be controlled by the workers themselves through direct participation instead of being run by Leninists, Stalinists, Castroites, or other ill-willed, power-hungry, bureaucratic cabals of evil men who betray revolutions. Unfortunately, this “pure socialism” view is ahistorical and nonfalsifiable; it cannot be tested against the actualities of history. It compares an ideal against an imperfect reality, and the reality comes off a poor second. It imagines what socialism would be like in a world far better than this one, where no strong state structure or security force is required, where none of the value produced by workers needs to be expropriated to rebuild society and defend it from invasion and internal sabotage.

The pure socialists’ ideological anticipations remain untainted by existing practice. They do not explain how the manifold functions of a revolutionary society would be organized, how external attack and internal sabotage would be thwarted, how bureaucracy would be avoided, scarce resources allocated, policy differences settled, priorities set, and production and distribution conducted. Instead, they offer vague statements about how the workers themselves will directly own and control the means of production and will arrive at their own solutions through creative struggle. No surprise then that the pure socialists support every revolution except the ones that succeed.

The pure socialists had a vision of a new society that would create and be created by new people, a society so transformed in its fundaments as to leave little opportunity for wrongful acts, corruption, and criminal abuses of state power. There would be no bureaucracy or self-interested coteries, no ruthless conflicts or hurtful decisions. When the reality proves different and more difficult, some on the Left proceed to condemn the real thing and announce that they “feel betrayed” by this or that revolution.

Not being able to defend itself is indeed an indictment of a societal structure.