Why was the crucifixion necessary ?

[Undeceived]

Of course all of that requires that the story be true.

If only you had some evidence that it was instead of nothing but the blithering of later writers.

There is enough evidence for you to choose to believe. "Proof" and "truth" are two very distinct things. No one can prove a historical figure, but they can believe they lived. Do you demand I show that Julius Caesar lived? Or do you already believe he did?