...or other facilities which are more obvious when you understand the difference between with script does in a consensus system... that it's not really performing computation, but verification of computation.
This is a very important concept to internalize. I don't think Satoshi realized it, and I think if he did Bitcoin Script would be very different from what we have.
In a future ideal world where arbitrary zero-knowledge-proofs are time-tested and have robust implementations, everybody except for the N entities directly involved in a transaction would validate a short, opaque proof that some computation took place authorizing the transaction.
If you're designing a better transaction system, you should design with that ideal in mind.