The death of Kim Delaney was a big turning point for him on this, I suspect. Though it was also a series of punches: Kim, then Murphy (Nightmare), then Susan, then Shiro. All of these were instances where somebody (usually him) kept secrets from others "for their own good" and it ended up screwing things over even worse than they'd feared.
The thing is, sometimes that backfires too. There are times when people really are better off not knowing, and times when they need to know.
For example, Harry didn't tell Murphy the truth about the Council or how the supernatural world worked until
Grave Peril. He was afraid telling her would get her hurt or killed.
Was he right to keep her in the dark? He might well have been, at that time. By the time he did tell her, Murphy had experienced her encounter with the
loup garou that changed her outlook radically. Before that, she was a lot less realistic about her options.
Imagine Harry tells the Karrin of the first two books that there exists an organization that maintains squads of killers, who consider themselves entitled to enter Chicago any time they want,
cut the heads off of children and teenagers at their own discretion, that he knows their names and of some specific cases, never reported it, and she has to leave them alone and not I interfere with it.
Do you think the Murphy
of those days could have stood to do it, or to accept that there really are people and individuals whom she has to treat as above the law? Or would she have done what she considered her duty (in the eyes of the law, it
would be her duty) and arrest Harry and try to go after the Wardens and expose/stop them?
If the later, stop and think what probably happens to her, to Harry, to the Murphy family, to others. The least bad outcome would be Murphy goes to prison on some framed up charge, and gets to be a cop behind bars. It could be far worse.
Even as late as
Grave Peril, she freaks out when Harry tells her he was present for the beheading of a warlock in Chicago, part of her wanted to go after them, and by then she had learned from hard experience that the supernatural was bigger than the law.
Likewise Susan. Harry held very little back from her, and what he told her led her to seek out more, and ended up destroying her. Susan would have been far better off if she'd never learned of the supernatural at all.
When to inform people, and when to keep them in the dark, is a hard choice and doesn't have easy answers.
