From the out takes I've seen on FNC, O'Reilly did not do well with the question in the first place. Moore asked O'Reilly if he would send his son to be killed. O'Reilly should have said that 1) it's an all volunteer army so he would not have been in a position to send anyone, and 2) our mission there is to free the Iraqis and in doing so prevent a possible future attack against the US. O'Reilly offered neither.
And yes, hind-sight is always 20:20. However, O'Reilly lost the offensive at that point which is something no talk show host should do, and he failed to regain it.