On the other hand, the Internet is black with the ink of people who think they understand physics but do not. Credentials do help you to distinguish someone who has a chance of knowing what they're talking about.
I mean, it's… true? My own (very highly upvoted) comment on the main thread of this article contains the text "I only took four lectures of General Relativity before I gave it up in favour of computability and logic", which is helpful context for anyone who reads it, because it lets the reader know in a fairly objective sense that I am familiar with some of the concepts of GR but am unlikely to understand everything in detail. You can't know whether someone on the Internet knows what they're talking about, but they can give you some of their context to help you decide. Admittedly "a good school" is not the most useful context, but it's better than no context.