My theory is that Fiat currencies and their central banks are beneficial only to the state, and not to individuals. And that for any system to be viable in the long-term, it needs to benefit individuals else they won't use it.

1.) To a first approximation, central bank policy consists of creating lots more money, all the time.

That is a bad thing for anybody holding the currency (everyone). Therefore these people (everyone) are incentivised not to hold the currency, and instead to hold a currency that can not be inflated away from them. For example, bitcoin.

2.) We're heading towards a cashless society. If the manifestation of a cashless society is one based on fiat currency, that means every single transaction and all money are subject to surveillance, censorship, and even seizure. By the state and by private companies.

Anybody who doesn't want those things to happen to them (everyone) is therefore incentivised to use a currency which is not subject to those things. For example, bitcoin.