Going off on a huge nerdy tangent but... people think that about anarchism because the violent dystopian image is what you would actually get in most scenarios.
Anarchism is the politics of ignoring game theory. If you study game theory even a little one of the big lessons is that cooperation at scale is incredibly hard, and that most highly cooperative states are highly unstable. A small number of defectors can easily collapse the whole system back to a more stable tit-for-tat or all-defect state. All-defect states, meanwhile, are often stable.
This probably explains why it took billions of years to get multicellular complex life. It took billions of years for evolution to figure out how to make something that doesn't instantly defect.
It's related to the second law of thermodynamics. An all cooperate state is highly ordered, and thus higher energy and prone to collapsing into a lower energy less ordered state.
A living system that wants to be all-cooperate is going to have to expend huge amounts of energy to maintain that state, which leads me to the final problem with anarchism: most anarchists I've read or met are at least to some degree anti-growth / anti-industry / primitivist types. That math doesn't math. If you want a society where everyone cooperates and is taken care of, that society is going to have huge energy needs, much larger than totalitarian-slum or crime-ridden-hellhole.
I mean, poor people use less energy for starters. Dead people use even less.
The last part is why all the most socially realistic depictions of societies like this are post-scarcity where they've mastered some kind of sci-fi energy source (cheap easy fusion, antimatter, tapping the zero point, etc.). They can create an all-cooperate utopia by using embarrassing amounts of energy to not just police and stamp out defection but render it unnecessary to begin with.