It has more to do with the fact that the state is, quite literally, the ability to do legalized violence. Not that these people have any actual coherent understanding of political science. The state, in order to be a state, must have and maintain a monopoly on violence.

The goal is to work towards a future where no violence from anyone is legal. Liberals don't believe such a thing is ever possible, therefore any communist who is using the state to attempt to achieve such a goal is therefore lying.

This is also where the difference between most Left-Coms and MLs lies. Left-Coms believe that you can simply abolish the state and the commodity-form wholesale, while MLs believe that the state apparatus must first be harnessed for the benefit of the working class, as it is a tool, to control violence and use it against the bourgeois (and more importantly not against the working class).

Anarchists (assuming they are principled and not simply liberals larping as anarchists) are on the same side as the Left-coms, they simply believe that a stateless society should be organized around small stateless producers, rather than industrialized economies of scale.

TLDR: Yes, all states are authoritarian, but only ML states exist around the idea that we should using the state apparatus a be moving towards a stateless future, whereas liberal states are more than happy to wallow in the current modern setup forever, as if states are an eternal concept, and not an extremely recent phenomena (relative to humanity).