What is a 'game expert'?

Over at Game Intellectualism, DapperAnarchist/Joseph writes a short blog letter asking: what does it take to be a ‘game expert’:

I’m pretty sure you know that the original Republic of Letters was made up of men (yeah, mostly men) with expertise in some subject - philosophy, law, natural science, history, whatever. This Republic of Bloggers is made up of… who? Experts in games? What then is an expert in games? … You’re clearly an expert, if any such thing exists. Do you feel like one? How do you think you became one? And do you think there are necessary things to be an expert?

I’ll be replying shortly, I’m sure other replies would also be welcome!