With some technologies, if you match attacker and defender effort you're safe, but not all of them. Nukes are the traditional example: if every person was a "nuclear power" we'd be dead within the day. But luckily there are bottlenecks to nuke creation that we can track.
What worries me the most (enough that I left tech to work on this full time) is bio. The amount of effort needed to defend against a pathogen can be many orders of magnitude higher than the effort needed to create it, and the upstream bottlenecks are both less limiting and mostly undefended. We've been safe so far because bio is very hard, but "rare expertise" as a gatekeeper is on its way out.
What worries me the most (enough that I left tech to work on this full time) is bio. The amount of effort needed to defend against a pathogen can be many orders of magnitude higher than the effort needed to create it, and the upstream bottlenecks are both less limiting and mostly undefended. We've been safe so far because bio is very hard, but "rare expertise" as a gatekeeper is on its way out.