Following my previous post - something I want to point out. The Bill Ayers thing is a subject that, if done right, I think could qualify as valid political discourse.
If McCain had launched his political career at, and then repeatedly teamed up politically with, an unremorseful abortion bomber, I don't think anyone on the left would dispute it's relevance to the campaign.
Who you associate yourself with politically speaks to your values and judgment. Those are valid issues to put on the table. And the Ayers scenario and the made up McCain scenario are not cases of association fallacy (or, commonly, "guilt by association"). Assuming Obama shares the same views as Bill Ayers would be an association fallacy. Pointing out Obama repeatedly teamed up with someone way out of the mainstream is not.
But, with people yelling "Kill Him!" about Bill Ayers at campaign rallies, the McCain campaign clearly hasn't handled this the right way. You can't blame a campaign for everything someone says, but they clearly fanned the flames that led to the possibility of such out bursts.
Also, since the campaign started hitting on the Ayers connection prior the the previous debate, McCain really should have brought it up, in an intelligent and discourse-respecting way, at the debate. Something like "Senator Obama: you present yourself as someone moderate and 'post partisan.' How then do you reconcile your willingness to freely associate yourself with, for political purposes, a whole laundry list of people way out of the mainstream, like Bill Ayers, Reverend Wright, and Tony Rezko?"
Of course, I'd really encourage McCain to take a different route. He could make the same point about Obama's judgment and willing association with unsavory characters - but without invoking the topic of a domestic terrorist (which is what gets the ignorant right into such a frenzy) - by asking something like: "Senator Obama: The American people know my ticket wants to reform Washington. You claim you want to work for reform as well. But why should the American people believe you since, in 2007 you endorsed Dorothy Tillman for re-election? The people of Chicago's 3rd Ward were able to see Tillman's corruption and vote her out office. Why weren't you able to see that she was corrupt?"