Clara made the wrong choice, but was painted as having been in the right. She singlehandedly condemned countless innocents on Earth to the havoc wrecked by not only the irreversible change in the tides, but in the subsequent bombardment of the surface. She had absolutely no way of knowing what would transpire. There wasn't a single hint that the creature would replace the Moon, nor that the debris would simply evaporate. She chose to allow the potential deaths of billions for the sake of a embryo. They never even suggested that the creature might be intelligent, or if it were capable of survival on its own. There's no dilemma here. What disgusted me the most was her last second decision to cancel the detonation. She left it up to a vote - democracy on a global scale, for what was likely the first time in human history, and overrode it. She knew better than the entire planet, because she had the means of deciding for them? That's goddamn fascism right there.
And this whole thing could have been saved so easily with a simple re-write. Instead of a dormant embryo, why not have an entire intelligent civilization living inside the moon? Then there's an argument to be had, actual ethical consequences to the decisions being made. Some real grey areas. Instead, we're left with a half-baked allegory for abortion? I can't even tell, honestly.