I agree with your overall point, that we're not dealing with two absolutes, you either centrally plan everything or you decentralise everything. The world we are inheriting, or will inherit, will come with issues and conditions that can only be solved by something that acts as a state apparatus.
>Non-centralized institutions are necessary to deal with major collective action problems, like for instance climate change
Funny, because I'd actually say that climate change is something that needs a central/unified/planned solution, rather than a bunch of decentralised solutions that would probably be counter-productive more often than not.
Things we need central planning/state apparatus to deal with:
>nuclear energy and accompanying infrastructure
>medical science and healthcare
>defense on a "national"/regional scale
>maintenance of ecosystems, land, fisheries, oceans, etc.
>standardisation of things like electrical appliances, and anything else that needs to interwork with other part
>standardisation of education (to some degree, to make sure everyone is sort of on the same level)
Other than that, everything can be decided on a local scale, by community councils or assemblies, or whatever, similar to how the Zapatistas make decisions and run their region.
The idea is that every autonomous region (to call it that) would be largely self-sufficient when it comes to things like food, water, shelter, education, and the basic necessities, while the rest would be made in cooperation with the other regions. Or that's how the whole libertarian marxism, libertarian communism thing sounds like to me.