> Ethereum nodes can in theory filter modifications to the smart contracts they execute.
This is the crux of the point, and as far as I'm aware is incorrect. A transaction to change a smart contract must be signed, a node cannot modify a transaction. A miner can in theory refuse a transaction to change a contract, but the only way to reliably prevent a change is a 51% attack. A node could refuse to accept a change, but it would fork the network and the node would be running a non canonical chain, which makes it pointless.
This is the crux of the point, and as far as I'm aware is incorrect. A transaction to change a smart contract must be signed, a node cannot modify a transaction. A miner can in theory refuse a transaction to change a contract, but the only way to reliably prevent a change is a 51% attack. A node could refuse to accept a change, but it would fork the network and the node would be running a non canonical chain, which makes it pointless.