Oh come on, we have to remember there are very smart people in the world who are Christians - and surely, if a bunch of teenagers could figure out such a basic flaw in their reasoning, then these very smart people would've seen it ages ago.
Obviously there's a deeper explanation we're all missing.
I, for one, am intrigued on how Islamic people can believe that Jesus was not crucified - even though it was drilled into me that his crucifixion was a major world event. And yet you have quite intelligent people who are Muslim, and yet don't believe this apparently 'fundamental historical fact' for some reason.
So who knows.