God has made it so that Princess Bubblegum will one day die. That her kingdom will be without leadership, that her people will suffer as a result. He built a world where death and pain are essential and inherent to existence. To be a good ruler, the Princess must defy God's intent. She must work as if the cruelty and indifference of God can be subverted by the acts of man (or radioactively mutated candy). That we can be better than our creator. That rather than succumb to the endless void, we can make a flame that burns forever. And if a few atom-bombs and psychic candy-sphinxs result along that path, so be it. No such sins compare in wickedness to submission and surrender to the cosmic tyrant.
I thought it was telling that her DNA produced an absolute monster, whereas Finn's DNA produced a hero that saved the world from eternal damnation. Is there some foreshadowing there? Who knows!