While trust is unlikely given the current state of politics, there is a better reason to not trust anything: the same reason you give up unnecessary privileges in a server jail.

Limiting trust doesn't just protect against malicious or targeted attacks - it also helps with plain old bugs. In general, limiting access and trust to what is actually needed is a good engineering practice.

Or, simply: we gave up on /etc/hosts.equiv (and .rhosts) a long time ago, and it would be a bad idea to repeat that kind of design mistake.