What Prevents Odysseus From Killing The Sleeping Cyclops?

The story of Odysseus begins in Homer’s The Iliad, but his second poem, The Odyssey, recounts the tale of Odysseus’ ten-year journey across the seas in search of the home after the Trojan War. For strategy and guile, Odysseus was favored by Athena.
After their long journey, the main character and his crewmates discovered an island where they decided to relax. They soon discovered a vast cave – the home of the enormous Cyclops – son of Poseidon – which was inhabited by a single family. The crew had no idea who lived in the cave, nor would they have waited outside for him if he did not appear immediately.
Odysseus and his fellow soldiers became the prisoners of the cyclops, he kept them in his cave day and night by rolling a massive boulder in front of the entrance. Every morning the cyclops would roll the boulder away for his sheep to exit the cave and then roll the boulder back. So if Odysseus killed the cyclops in his sleep then they would forever be stuck in the cave, because they didn’t have the strength to roll the boulder away themselves.
What Odysseus did instead was blind the cyclops and when the cyclops went to open the boulder for his sheep to go out, he listened for the footsteps of men among the sheep, when he heard non he was satisfied that the prisoners had stayed inside the cave.
However, they held onto the bottom of the sheep and the sheep carried them out of the cave and so they escaped.