Then he fingered Ventura. He was burning the source. That's a devastating blow to journalism. Because these things don't exist in a vacuum. They have repercussions for journalists everywhere.
Isolated incidents do lasting damage.
High-profile instances of journalists turning their backs on promises of confidentiality are, mercifully, rare. One case took place in the early 1980s, when editors at the St. Paul Pioneer Press and Minneapolis' Star Tribune ordered reporters to identify an anonymous source who had provided damaging information about a political candidate. They resisted, but ultimately succumbed to their bosses and identified the tipster in their articles. Predictably, the source promptly lost his job. He sued the papers for fraud and breach of contract.