Re: Aikido does not work at all in a fight.
My main problem with those who continually challenge any martial arts practitioner is that many of these arts have death or debilitating blows that you simply cannot apply in a sparring situation. When I studied kung fu, we practiced full force strikes on a head/torso dummy because these moves were meant to kill or horribly maim. You cannot apply these is a "friendly match" like you might with BJJ because you can grapple and take someone down with 3/4 of the technique before doing serious harm.
I do not know Aikido but from all of the demos I have seen, it's pretty clear that applying these moves in real life would render the attacker maimed (dislocation or broken arm) that would pretty much stop a fight cold unless the guy was on PCP or something.
I totally respect these demos perhaps because I have trained in other martial arts where you could certainly imagine what would happen if you applied the techniques full force.