You nailed it. A person’s response is an admission or rejection. I too would respond with outrage at a false accusation, not defensive like their statement. This is like Larry Craig pleading guilty instead of being outraged over being “falsely accused” of cruising for gays. This is like OJs lack of outrage at being “falsely accused” of killing his wife.
On their statement alone, I think the McCanns are guilty. I agree with you.
Speculation is not evidence. Opinion can sometimes convict innocent people. Lindy 'The Dingo got my baby' could tell you something about that. Australian public opinion was totally against her. There were theories she sacrificed her baby in some weird ritual on Ayes Rock...there was no way she could get a fair trial after the media was through with the story.
I try always to leave the door open for doubt and the possibility of innocence.