This is extremely widely misunderstood, one of those rampant FUD topics.
Archive nodes in Ethereum are almost completely superfluous.
An Ethereum archive node is not the same thing as a full node.
Archive nodes add zero extra security to the network. They are only useful for historical analysis of past states.
100% of the blockchain information is stored in non-archival full nodes.
The Ethereum system is a series of transactions that modify a state. The system is completely defined by the transactions. The latest state can be derived from them.
An archive node is a node that stores all past states for efficient retrieval.
...so, we're back to trusting a set of centralized parties, then? What if those get wiped? Altered (though that seems less likely)? Is such an archive a fork vector?
I wrote a blockchain explorer on Bitcoin as a technical exercise, and the intermediate state thing caught my attention, too. If all copies of a block disappear and all you're left with is a hash, what do you have? A complete blockchain?
