I defnitely agree that we should not use the "MMA is bad, but not as bad as ..." argument. No good comes of that. I like to use the 'focus' argument too - in ball sports, injuries happen all the time, some actually quite serious, eg. knees and ankles blown out, bones broken, concussions etc.
These things generally happen as 'incidental' to the main focus of either the injured player or an opponent - by that I mean, a footballer will be trying to hold onto the ball, or get out of the tackle from one player, or stay standing, or even all three, when he will twist his knee, or get blindsided by an elbow from a player he didn't see coming, or his ankle will get crushed under the weight of his tacklers. My point is: the players focus is NOT on self-preservation - he is focussed on a multitude of other things.
Combat sports put the combatants into a situation where they have 2 things to focus on - protecting themselves, and attacking their opponent. That's it. Nothing else to get in the way. It's always the punch you don't see that knocks you out, and it's more often the 'punches' you don't see in ball sports that cause the injuries. When your focus is on defense, it's easier to not get surprised.
The prevalence of these serious injuries in these 'non-combat' sports precludes them from being called "accidents', or "incidental". The evidence suggests that MMA does NOT have these injury problems - all available evidence points to any damage sustained is confined to superficial only - ie. cuts, bruising, swelling.
MMA also has many avenues available to end a fight, such as tapping, verbally submitting, ref or corner intervention. Their is no stigma attached to 'quitting' - it is honourable to tap out when being beaten.
I also think we should only refute the 'repeated battering of the brain' argument in response to specific (stupid) allegations such as the Muhammad Ali analogy made by the AMA in the Ten news piece, by stating the number of shots to the head is always a low number, as serious shots result in an early end to the fight. Otherwise we should never bring it up.
My 2 cents... ;-)