Your typical professional Republican may not be the sharpest set of false teeth in the Polident commercial, but even Republicans aren't dumb enough to suggest that Obama used to stop by Ayer's headquarters after school and assemble bombs when his paper route was finished, and still manage to get home in time to watch Scoobie Doo.
Nor should it necessarily be suggested that Obama shares Ayers' erstwhile desire to blow things up. (Let's extend to Ayers the benefit of the doubt that when he states that he now abhors all forms of terrorism, he means it, at least at some level.) So if we remove those perspectives from consideration, what can possibly be the problem?
Quite simply, there are some forms of invidiousness that, once committed, forever strip away any right to be considered morally eligible for public discourse.
Take the example of David Duke, former Grand Wizard of the Ku Klux Klan, another terrorist organization. I remember seeing him on CNN's "Crossfire" when running for office in Louisiana as a Republican. He looked nice and gentlemanly, in a nice suit, and tried to present an image congruent with the idea that his days as a white supremacist were over. I don't think anyone bought it. But it was really beside the point. Someone with a past like Duke's should be atoning for it, not running for political office and trying to direct the body politic. To me, it's the political equivalent of the Rev. Jimmy Swaggart's struggles with frequenting prostitutes. "None of us are without sin," one could say in his defense. Absolutely. "That means he is still a Christian." That's a distinct possibility. "Let's allow him to continue his ministry." Bzzzzt. Wrong answer. Mr. Swaggart's career as a minister should have been over for good. He should not be preaching to the pews. He should be sitting in one.
Hypothetical situation: imagine for just a minute that John McCain had been introduced as a political candidate at a gathering held at David Duke's house. Do you think the mainstream news media would give McCain a free ride on that? I don't think so, Tim. But the mainstream media, and even Wikipedia, wear that well-known, disdainful "Who farted?" expression when conservatives bring up the fact that Ayers hosted such an event for Obama.
The proper objection to McCain associating in any way with David Duke would not be that McCain necessarily hates black people, or that McCain participated in lynchings when he was eight years old. The objection would be that, to be qualified to lead this country, you are simply required to know who the bad guys are, and to abhor them. And even if the bad guys have repented to some degree, you still can't publicly dishonor the folks whose lives they damaged. A presidential candidate needs to be revulsed by Duke's past and should refuse even to grant an audience to him. The candidate needs to show that the things that ought to repulse any civilized man also repulse him. The proper response to a David Duke is to pray for him and help him in any way that Christ would approve, but never to clink ceremonial coffee cups with him at a political soiree.
Same with Ayers and Obama. Ayers did some despicable things when he was younger. Maybe he's sorry. Maybe not. That's between him and God. But either way, Ayers has no business participating in any activity with any political candidate, and Obama had no business allowing himself to be promoted in such a manner. It showed, at best, a surpassing moral obtuseness -- as if, in the circles where Obama hangs out, having been a domestic terrorist and bomber is no big deal.
Democrats may not like it that Republicans are always trying to portray them as unpatriotic, but that don't have to light the fuse on that particular bomb.