Years ago I took the Buddhist precepts with the Kwan Um School of Zen and the first precept was pretty clear –
I vow to abstain from taking life.
The commentary on this precept states that:
Killing roots out our seeds of love and mercy. To kill another is to feast on one’s friends and relatives. Some day we shall be in one of the three painful realms in payment for our killing, for it is by bestowing life that we receive human life in return.