This is why we have firewalls. My pfSense router e.g. blocks external access by virtue of it being a firewall with sensible defaults.
All routers w/ firewalls will/should have them.
All routers w/ firewalls will/should have them.
While I get that firewalls are probably safe like 99.99% of the time… I’ve gotta say, I just don’t trust software to not have vulns of some sort that someone important already knows how to break. So eg for a corporate network I would be hesitant to do this, for my personal network not so much (unlikely that a 3 letter agency gives a shit about what I do).
Additionally. Firewall changes can sometimes fail for whatever reasons so you might have accidentally exposed a node publicly for some time.
Making those nodes not reachable from the internet seems prudent. It’s like your office building has a public address but your office assignments don’t need to be public.
For the whole world there is absolutely no difference betwen routable address, non-routable address or even an absense of the machine... behind a firewall with drop all on a public interface.
You are correct in theory. What you don’t seem to be taking into consideration are firewall vulnerabilities or other unknown things that could happen that make it different from a practical standpoint.
I started an ISP from the ground in 1996. I’ve seen a lot of weird stuff. You seem to just hand waive it away like firewalls are this perfect bastion of security.
Maybe you have more experience than I do?