[throw0101a]

> Who exactly is going to route/send an RFC1918 address to an Internet gateway?

The GP is talking about 1:1 'basic' NAT:

* https://datatracker.ietf.org/doc/html/rfc2663#section-4.1.1

[Dagger2]

The same problem applies to masquerading. Routers are happy to route packets they receive, and NAT (in whatever form) isn't the tool you use to drop those packets.