Let me refine that a bit more, if I may. Karsnia told him the truth about his own intentions and let Craig make whatever he wanted out of it. Nothing prevented Craig, who is a 62-year-old law maker, not a naive 16-year-old skateboarder, from recalling that arrest reports pass through many hands as they wend their way through the criminal justice system.
Over the many years of Craig's career, he has seen many, many colleagues go down because of leaked information.
Pretty nuanced version of "truth." I must have missed the part where Karsinia said, "Senator Craig, you are a public figure. This will be made public whether you plead guilty or not guilty." Instead he said,
DK: There'll be a fine. You won't have to explain anything. (inaudible) I know. LC: Right.DK: And you'll pay a fine, you be (inaudible), done. Or if you want to plead not guilty, ah, and I, I can't make these decisions for you.
...DK: Okay. So we'll start over, you're gonna get out of here. You're gonna have to pay a fine and that will be it. Okay. I don't call media, I don't do any of that type of crap.
Karsinia is clearly trying to use the threat of publicity as leverage to get a guilty plea, though he knows that the publicity is inevitable whatever the plea. That, plus the paucity of evidence of Craig's sexual intent, is why I think this was probably a police scam, that used the threat of publicity to extort guilty pleas out of both guilty AND innocent men.
You are certainly right that Craig should have known better, but obviously he did not. Pleading guilty may have saved him some money, but his career as a senator was over whatever he did, and it would have looked better in the long run for him to have plead not guilty. However, I suspect that most men who lead non-public lives would be better off pleading guilty even if they were falsely accused. There is less likelihood that people will learn of the accusation, and it is a lot cheaper.
The police should require much, much better evidence before they ruin someone's life.