But who says legitimate whistleblowers have specific rules under which they must do it? (E.g. they must only enter into employment or servitude with zero suspicion of employer or zero intent to leak information of any wrongdoing observed? Isn't that against the very principles of whistleblowing, and even potentially legal protections under whistleblowing laws?)

His actions are only seen as a 'sin' if you already agree his whistleblowing wasn't warranted.