Pin the Problem on ABC?

Day two and the Democratic debate fallout continues. Turns out the lady who asked Obama the question about the Flag Pin, in a prerecorded tape made by ABC, had already told the New York Times that she could not support Barack Obama--because of his sometimes aversion to wearing flag pins. So, it wasn't really a question from an undecided voter as much as a jibe from someone who had already declared publicly that she was against Obama. Or as Howard Kurtz puts it:

In other words, in staging a debate between Obama and Hillary Clinton, ABC deliberately gave a platform to a Pennsylvanian who had indicated in advance that she could not support one candidate. McCabe's question, which was expanded upon by moderator Charlie Gibson, forced Obama to defend his patriotism.

There is nothing that says undecided voters are the only ones whose opinions matter, or the only ones who get to ask questions, or that someone who has previously voiced an opinion is disqualified. But in this day and age, who at ABC thought they could pull something like this off without controversy? Why do such an elaborately pre-planned woman-on-the-street? Why didn't the moderators just ask the question themselves?