For some unknown reason many layfolks believe that C.S. Lewis is the end all of Christian Apologetics, despite having worse arguments than real Christian apologetics. One of his more famous arguments was the Trilemma: Lunatic, Liar, or Lord. Basically he held that Jesus was either a Lunatic, a Liar, or God. To rule out Lunatic and Liar he basically asked why are you saying such mean things, and then suddenly concluding that Jesus was God. I have no clue how anybody could be bamboozled by this nonsense, but it's apparently as popular as his "atheism is just too easy" argument.
Even skipping the clear problems with his arguments against the first two L-words. We are still left with a false 'trilemma'. We aren't able to conclude that the story is just fiction. It fits perfectly well into the fiction category. The story is written such that it falls perfectly well into the Hero's journey. It makes much more sense from a mythicist point of view than from one based in reality.
Either Hercules was a lunatic, liar, or son of Zeus. Clearly he wasn't lying or crazy. Therefore, he's the son of Zeus. Zeus exists.