This is a bit of a tangent but still very interesting in my opinion.
I refer to the passages you posted:
Genesis 9:5 And surely your blood of your lives will I require; at the hand of every beast will I require it, and at the hand of man; at the hand of every man's brother will I require the life of man.
Genesis 9:6 Whoso sheddeth man's blood, by man shall his blood be shed: for in the image of God made he man.
At first glance it appears that God is saying that if you kill a man then a man must kill you and then that man must be killed by man because HE killed a man, etc., etc., etc., ...
But I'm thinking of three possible reasonings here:
1. That God didn't want anyone from Noah henceforth to commit murder of another human being otherwise a terrible tet for tat would ensue.
2. That God was letting man know that self defence was acceptable to Him in terms of being allowed to shed the blood of someone who seeks to shed yours.
3. That God expected everyone (every man's brother) to participate in the shedding of the original offender's blood in order to let themselves and others know that there is a grave penalty for murder. Of course this would have to presuppose that God had leniency/forgivenes to those who were tasked with shedding the blood of the original offender.
The last one was just a thought but personally I think the second may be more likely since God also says that beasts may shed the blood of man just as man may shed the blood of the beasts. In otherwords that as it is ok for man to kill the beasts for food or defence so too can the beasts kill man for food or defence. Of course in the case of man vs man I think God is referring to selfdefence only, not food. :)