A wise man once told me, "Never step into a fight you've been invited to!" This situation was more like, "Never step into a fight you've been invited to, blindfolded with your hands tied behind your back."
The invitation was extended explicitly to make the NRA look bad; it was a no win situation. If they accept the invitation, it affords Obama the chance to make them look bad in his reply to their one question. If they refuse, it gives Obama the chance to rub their noses in it for declining the invitation. In my opinion, there is absolutely no doubt that the NRA took the best course of action in this matter.
By allowing only one pre-approved question, with no rebuttal to his response, Obama is clearly given the upper hand to sell his agenda. Regardless of what question one posed, he had time to prepare a deceitful response to cover his [beeep], serve his cause, and lead the no-minded sheeple down the path of righteousness. In not allowing rebuttal, those posing questions were not allowed to point out the fallacious nature of his response to their question. It was that simple.
The event was scripted to make him look intelligent; which he's not. Make his cause appear noble; which it isn't. His actions appear just; which they aren't. And, his proposed Executive Orders appear effective; which as we all know, they won't be. It wasn't a town hall meeting; it was an infommercial, it was designed to sell his anti-gun plans. With a tear or two squeezed in, to solicit emotional response from the mommy minded no-minded dweebs. If they had shown up, the NRA would have simply had fingers of blame pointed at them all night, with no recourse in addressing whatever Obama threw at them. They did the right thing in abstaining!