One small example of the core d/acc thesis (improving passive defensive technology improves safety and at the same time improves freedom and most other properties of social organization that we care about) is soundproof walls. We used to have much weaker soundproofing, and we had much more restrictive behavior rules, disputes (both inside families and between them), evictions, etc. Later, we solved that problem by making and deploying better walls, and now this is an issue that we all have to worry about much less. What are the "soundproof walls" of the 21st century that we have not yet built or sufficiently deployed?