One can say “non-capitalist society” yet mean that capitalism is the only thing that there ever is. Capitalism is a way to look at things, and it doesn’t require a modern society—social capital and economics of prestige is a thing since forever[0].
Indeed, in all large-scale supposed “non-capitalist” societies today there is capital—it doesn’t stop being so if a few people use unlimited power and oppression to install arbitrary rules and restrictions on capital for others without having being subject to any checks or balances themselves; it just becomes more contrived and perhaps perverted.
Some would probably say that it’s the infectious external influence of other capitalist countries that precludes full abolition of capital, but another way to look at it is that said external influence is in fact what gives such a regime life in the first place—i.e., if you remove the agitating antagonistic existence of “capitalism”, the pretend “non-capitalism capitalism” would not suddenly turn into a perfectly “non-capitalism non-capitalism” but rather revert to capitalism, regardless of whether it would be called so or not or whether it would happen violently or peacefully.
Yes, and I can even bet that unless a species is a hive mind, any intelligent species will have something like capitalism. The inverse is that to enforce a non-capitalist system, you have to brutally shape a society into something that is like a hive mind.
This seems true from our experiences attempting to implement non-capitalist systems in large societies. I think there could be a caveat for very small societies, especially those voluntarily joined, in which sharing goods and labor is possible with democratic modes of conflict management. There are also non-democratic capitalist systems that resort to extreme repression in order to resolve or suppress internal conflict. At scale, I agree no other economic system seems as compatible with democracy and individual choice, but as recent history has shown in Russia and China, capitalism itself doesn't seem sufficient to give rise to liberty.
