Legal theorist: Governments should not be allowed to use the personal diaries of an individual who is the subject of a criminal prosecution as evidence against that individual.
Conclusion
Governments should not be allowed to use the personal diaries of someone as evidence against themselves in a criminal prosecution.
Evidence
A diary is a silent conversation with oneself, equivalent to speaking to yourself or keeping your thoughts to yourself.
Evaluate
By analogy, it sounds like author is assuming that .
She's saying, whether it's a diary, muttering to oneself, or just saying your thoughts "out loud" in the privacy of your mental theater, it's all the same --- these are your thoughts, a private conversation between you and you.
She apparently thinks this type of conversation is inadmissible.
Goal
Since our focus on Strengthen + Principle questions is the Conclusion, we want to remind ourselves what kind of idea we're trying to prove. We're hoping to support that .
So whatever principle we pick to support this claim should sound like a principle about what governments should / shouldn't be allowed to use as evidence in a trial.