What is it with this concept of "(un)trusted servers" that people throw around here all the time that seems to build on the assumption that the world consists o

What is it with this concept of "(un)trusted servers" that people throw around here all the time that seems to build on the assumption that the world consists only of entities that are to be distrusted and those that should have full access to and control over all your information and resources? No, just because I don't expect my client to kill me, does not mean that therefore there is no reason to be concerned about a rogue employee of theirs being able to gain access to any other of my clients' servers that I have access to by patching an exploit into their MySQL server. Nor is it reasonable to assume that everyone is on top of their IT security and their infrastructure is only under their own control, and that includes your own organization once it grows beyond one or two people. If that is the kind of mental model you are working with, your IT security probably is shit. Even the slightest external vulnerability anywhere in your systems or the systems of people whose systems you access/(co-)manage is going to grant an attacker total control over your organization if that is how you manage security.