This is true, but ...

... you can analyse this in a different way: think long term! The more successful you are in your job, the more you will bump into the same people again and again later, sometimes a decade later. Somebody else abused your trust by talking to HR, hence you could decide on the simple policy of never trusting them again, and cut them out of your high-trust network. Some fail your trust-related tests, some pass. Use this information wisely. (Note that an alternative policy is not being too history-sensitive, and let bygones be bygones.)