What they add is that a real human being is behind what they typed
I have never doubted that real human beings are behind the thousands of posts on WebmasterWorld.
And I have never considered it remotely relevant (or interesting) what any of them looked like.
It is clear from the many avatar-toting services I am familiar with that some people like to upload a genuine photo of themselves while many others prefer to use a photo of a celebrity, a cartoon, a graphic, an abstract, or any other image they consider amusing (but which others may not find at all funny).
Short of enforcing a policy involving certified passport photographs (possibly updated every few years) the idea that an avatar would identify the author as "a real human being" is somewhat far-fetched.
I do not intend to be anti-social in pointing this out.
I've found that most people don't even bother uploading avatars
With respect, that is not a particularly compelling argument in their favour.