Although I understand your hesitance to discuss the epistemology of truth on a forum such as this, I would suggest that this is precisely the place to have such a conversation. (“Capital T”-Truth might be beyond our scope, though.) What I’m trying to say is, this place, a place for government employees, should have no qualms agreeing to this maxim: it is wrong to lie.
From that maxim flows that it is right to always speak truthfully. Assuming perfect knowledge, there is no justification for a public servant to say untrue things.
Of course, no human possesses perfect knowledge. (Well, maybe the Vice President does.) But your question is not, “Do government communicators make mistakes?” Your question is, in two parts, “Can spin be ethical and do we ever not spin?”
First, I’d like to suggest a definition for spin. You mention belief and context, so I would offer this:
Spin is knowingly withholding context in the interest of belief.
So, do we ever not spin? Philosophically, I have to say no. In fact, I think it’s arguable that spin may be a natural defense mechanism against that perfect knowledge problem. It must be apparent to any introspective person in a position of authority that, sooner or later, they will be speaking with a deficit of knowledge. Spin lets leaders speak without jeopardizing their authority. In other words, if it’s impossible to speak the whole truth, spin lets us speak at least part of the truth.
Is spin, as I’ve conceived it, ethical? Perhaps not. Ideally, no one should speak without full knowledge, but then no one should ever speak. (Indeed, religious authorities for millennia have come to just that conclusion.) You and I, however, are not monks. Like any other sort of human imperfection, I think it’s only unethical if undertaken maliciously or negligently. It is not wrong to be wrong.
What makes spin work in the real world is that none of us ever get to tell just our side of the story. Many sides are being told and, perhaps when taken altogether, the multitude of perspectives equal the whole truth. It isn’t wrong to provide your, or your boss’s, point-of-view, but it is wrong to prevent anyone else from providing theirs.
To me, this is the rub: The question we should ask is not, “How shall we spin?” but rather “In whose voice shall we speak?” What you say is determined by whose voice with which you speak, so before you hit send on that email ask yourself, “Do I really know who I’m representing?”