Falling back to discussing definitions or other meta arguments is really a kind of cop out the way I see it. It's usually employed when people are not able or willing to partake in the discussion on the level it's at, so they take a step back and formulate meta questions instead. It doesn't take much knowledge to say "but how?" or "how do we define this?" or even stuff like "how do we know anything is real?", so it's kinda cheap, I think.
Sometimes such posts shed light on important problems and solutions that are found on higher levels, but mostly not .. at least not when discussing on forums.