It's definitely a policy, in that it's a design-decision that could be changed to make it operate differently. For example, if a good majority of a crypto-currency's miners elected to fork to a new policy, then it'd just happen.

And cryptocurrency isn't really about lacking a trusted-party so much as decentralizing the trusted-party. Which might sound pedantic, but it's an important distinction: there can be an authority that makes decisions, just it'd be decentralized.

Future crypto-systems, e.g. probably a next generation that'll replace early systems like Bitcoin, would probably take a smart-contract approach. For example, a payment could be reversed under conditions encoded in a smart-contract.

A well-developed system would likely end up including a system of checks-and-balances, appeals, manners of collecting evidence, etc., where trust is decentralized.

For example, most folks would generally agree that a mature, well-developed system should allow someone to recover funds extracted from them under threat-of-violence if everyone agrees that that's what happened. That current systems are too limited to make such an obviously-desirable thing happen is an obvious non-ideality. Once someone makes a good system that fixes such problems, in a generally agreeable way that people can trust, it'll likely become a preferred system; it and its clones, etc., would displace older systems, and this whole no-reversible-transactions thing would become a minor footnote in early history.