Earlier quoted context omitted.
I guess I mean, the gist only motivates the use of globally-routable addresses for externally accessible services. If a particular service/device isn't going to be accessed externally, there's no need to give it one.
A big part of why I see people talking past each other on this is, IMO, because the solution that seems ‘cleaner’ depends on one’s mental model of networks / IPv6. These can and do differ. One person’s “I need justification to have non-globally-routed addresses” is another person’s “I need justification to have anything else”.
There's a belief among some ipv6 proponents that the Internet should primarily be p2p services, meaning everything is globally accessible. This would imply it's not ok for NAT or default-deny firewalls to be common practice.