"Argument by authority" is not a fatal fallacy. The key insight is appealing to an irrelevant authority. For example:
Oprah says heartbleed is not a problem.
Maybe she's right, maybe she's not. But appealing to her authority doesn't help because she's not an authority on this topic.
Colin Percival knows a lot about FreeBSD security.
This appeal to authority is much stronger, because Colin Percival is the former FreeBSD Security Officer, runs a security-conscious SaaS, provides security review and consulting services, publishes on security matters, has corrected major companies' security errors and has developed novel cryptographic algorithms.
>The key insight is appealing to an irrelevant authority.
This is true, but the authority is almost never relevant to forming a valid argument. It's just a shortcut. Take the following:
"X is not Y. I am a subject expert on X and Y."
It may be true that X is not Y. It may also be true that I know everything there is to know about X and Y. However, it's a completely invalid argument. There is no evidence provided about why X is not Y.
If someone questions why is X not Y, providing more evidence of authority does not contribute to the discourse. It is definitely a fatal fallacy if you exchanging in meaningful discourse.
If you are just looking for general knowledge on topics you are vaguely familiar with, receiving knowledge backed by statements of authority is okay. But that's okay because you aren't actually arguing, you are just seeking clarification and knowledge.
