What is more precious than your life, and what loss could be more extreme than the loss of your life? What treasures could possibly compensate that loss?
Life is the most precious thing you have, that any sentient being has. From it, all other things and experiences flow. Thereby, what theft could be more extreme than the theft of what is most precious, the theft of life, any life -- intentionally taking a being's life?
Exhibit A, Stop Stealing Food, the case (an incomplete work-in-progress) for theft-free meals:
The Brahmajāla Sutta -- All-embracing Net of Views (translated from the Pali by Bhikkhu Bodhi)