The moral arguments were not used in the debates...since the questions are controlled by the moderators. If President Bush had tried to drag abortion into every question, the way Dr. Keyes does, he would have looked like a fool, been accused of pandering to the right wing, and LOST. As it was it was close, due to democrat cheating, the DUI, and network blackouts of Bush for over a month after the democrat convention.
As far as the Keyes, McCain, Bush debate, I do believe there was discussion at the time about whether the networks would carry it if Bush didn't show up, since he was the frontrunner. I don't have a source for that except for my memory, so you will have to take my word for it or not.
You are right -- the networks were not going to carry the debates if GW did not show up. If keyes wouldn't have showed up the debate would have been between Bush and McCain and if McCain didn't show up it would have been televised between Bush and Keyes and if Bush didn't show up no debate -- no television!
The debates were not the only place to discuss moral arguments. And, of course, there would have been many ways to bring it into the debates.....trade with China, for instance, or other foreign policy matters. But then, in the case of abortion (which is not the only moral crisis we are facing), was not on Bush's radar screen.
And its obvious we won't agree over why the election was close, either. :)