In this context, he's not a "source"--he's the subject of an article. Using the subject's full name is one way to prove to your readers that you're writing about who you claim you're writing about.
But it doesn't prove any such thing. He's writing about "Scott Alexander". All discussion of SSC that you will encounter will refer to "Scott Alexander". Claiming that "Scott Alexander" is really "Scott Somebodyorother" does not enhance the credibility of the article in the least. Rather the reverse, since it would make one wonder about the objectivity of the reporter if they for no reason cause massive damage to their subject, and his patients.
