I don't quite follow you. Yes, we can't prevent keys from leaking here and there, which could allow malicious actors to cause some damage, but we can reduce its

I don't quite follow you. Yes, we can't prevent keys from leaking here and there, which could allow malicious actors to cause some damage, but we can reduce its impact by making keys short-term (as we do today with TLS certificates) and capability-restricted, i.e. you would not be able to change highway speed limit with a road worker key and you will not be able to use a key generated for city A in a neighboring city B. And you probably will be able to use a leaked key only once, since after an illegal usage is detected it will be quickly revoked. Plus it will be clear whose negligence has caused the leak, thus responsible people/organizations can be held accountable, which eventually should improve cybersecurity level (at least a bit).