Even the script can't stop a user from copying data from one partition to another. So even if Ethereum only runs authorized and vetted scripts, this afaics wouldn't totally ameliorate the issue.

Edit: Of course (external) I/O from scripts can input to other scripts in a myriad of cascade and permuted entanglement.

When I write 'external I/O', I mean differentiated from referencing some data on the block chain as an input, e.g. UXTO. You see that for asset exchange, the data is deterministic because all I/O must sum to 0 and the directed acyclic graph assures us there is no recursion of the state.