Which text of the bible are you referring to? The original Hebrew text does not list the commandment as "Thou shalt not kill", but rather the literal interpretation is "Thou shalt not murder".
The difference in the interpretation is the sole and exclusive reason so many religions justify "Holy Wars" and add religion where convenient to have the ends justify the means. Any act done in the name of God is justifiable according to any number of religions.
Exodus 21:23 is taken directly from the Code Of Hammurabi circa 2250 B.C.E.
The Book Of Exodus historically begins circa 1490 BCE, or 750 years after the Code Of Hammurabi was written, and covers a period of roughly 400 years.
What is or is not granted under the authority of God depends upon one's beliefs. There are those who believe the Bible was written directly as the word of God, those who believe the Bible was written by man with the Divine Inspiration of God, and those who believe the Bible was written by man alone.
Your post is grossly inaccurate in that it assumes that all members of this forum subscribe to the same religious beliefs and values you subscribe to. That is simply not the case.
Or to simplify the entire discussion, there is supposed to be a separation of Church and State, per the United States Constitution. Therefore, any powers granted by the Bible are independent of, and inconsequential to any powers granted by the laws of the United States.