"Have you seen a laser beam reflected from the moon?"
Yes. Hell, I've done it as an amateur astonomy experiment.
"Why is it that re-building the Saturn-5 is impossible today?"
Because they destroyed the jigs and other tooling necessary, because nobody makes 1960s-vintage computer hardware anymore, because nobody writes code for 1960s hardware anymore (and they didn't save the source code), because the Saturn V was designed and built before environmental regulation ran amok...
If we still had the Saturn V hardware, it would be a possible to re-equip the system with new computers running modern code. If a B-52 can still fly after all these years there is no reason why a Saturn V could not also.
Your point about the Jigs, Tooling & Prints being destroyed is the real reason.