If we assume the story of creation is literally true (let's assume that for a second so don't disagree) and believe Adam and Eve procreated and had their sons Caim and Abel - And then were expelled from paradise - So... Since there is no other human being to procreate with, that means we all inevitably descend from incest.
My question is - Why is incest a sin if we all come from incest?
My question is - Why is incest a sin if we all come from incest?

Whoever fights monsters should see to it that in the process he does not become a monster. And if you gaze long enough into an abyss, the abyss will gaze back into you