> Would you risk getting in legal trouble for publishing a way to do bank fraud (for example) - assuming you gave some reasonable timeframe for disclosure?

Of course you would. The bank would call the FBI and tell them you're hacking the bank, and the FBI would then knock down your door, tear up your house and drag you away. The system would then do everything it could to represent what you did as a crime, and if you are lucky you get away with only a year in court, many thousands in debt and your name dragged through the mud.

tl;dr The actual legality of an action is only tangentially related to how the legal system will be used against you in response to it.