I have been following this thread with interest. I like when boats get rocked.
My small point is, you keep refering to aikido within the context of fighting. Aikido doesnt teach us how to fight, so you are right it is not effective in a fight. But it is very effective in not fighting.
Fighting is all about perspective, two forces pushing against each other...
If one of the forces refuses to push back or push in the same direction then their is no fight. One side could have the perseption of a fight while the other the perseption of harmony. no anger no strength required. just movement. So yes, if aikido is attempted to be used to fight then it defeats the whole point of aikido and destroys its effectiveness.
Aikido is not about a series of techniques designed to hurt or damage or whatever, it is about a principle of none resistance. Which is the reason it is often refered to as the art of peace.
as for the person sitting in the aikido punching him in the face... well... emmm... if the principles are being applied then it would NEVER get to that point. but if it did then I guess one of the main points in throwing in aikido is to get my centre below that of the attacker... you cant get much lower than under his butt....