Nick Szabo, here, is demonstrating, and recommending, handwaving as a security strategy.
He conflates a metaphor people can "understand" (locked doors) to support the idea of censoring specific bitcoin transactions at the mempool level.
But filters aren't locks. They aren't even doors. They are fences in an open field. They don't prevent trespassers, they increase people walking on the grass.
We already know how to censor bitcoin txns we don't like, because we already do it successfully! Miners know there are certain poisonous, yet valid, transactions. Through meatspace, they enforce exclusion of such txns.
Sadly, this whole "spam" "war" requires Bitcoiners to take a ride together that ends up supporting the idea of miners being heavily regulated by governments, and the idea that we must be good at censoring txns we do not like.
Because, unlike pleb nodes, it is miners that decide what gets into Bitcoin. No one else.
Arguing policy is pointless, just make the config you like and convince miners to run it...
...But if you do, know that you are doing evil, and acting as useful idiots for the state.
