The case in this passage is the proper response to an insult, or very minor injury (a slap on the face). Not to a threat on one's life, family, or country.
or following the interpretation "thou shalt not kill"
This is correctly translated, "Thou shalt not murder" as has been stated above.
then in the end this may be precisely why your God allows one to sin, but then ask forgiveness.
Shall we then sin, that grace may abound? God forbid.
We are, after all, only human, my friend. Only one, by your lights, has been perfect. And he forgives. Godspeed.
Nevertheless I live, yet not I, but Christ liveth in me, and the life which I now live in the flesh I live by faith in the Son of God who loved me and gave himself up for me.
Forgiviness is no license to sin.