This is a perfectly sound logical argument. The logic problem occurs when you use the conclusion to support the premises. If Graham Christian questions 1 and 4 based on his own fairly extensive experience and knowledge as a martial artist, and Chris Li raises IHTBF, this does not undermine Graham's argument, because IHTBF is based on the premises which are being questioned. To use IHTBF to support the premises is circular logic.
So if I were to question your
abilities in Aikido based upon my fairly extensive experience and knowledge your response would be something other than "You haven't met me, so how would you know?".
None of what I post here is supposed to be a logical (or even illogical) proof - it's just shooting the breeze.