The bronze serpent seems to be the object of faith or God's provision for those who would seek His deliverance. Changing the bronze serpent from an object used by God into a subject of worship reflects the practice of serpent magic which can be observed in ancient Egypt. This episode reflects the belief that the spoken word has objective reality and power, an idea which is common to the Bible. In a later account in Numbers, Balaam is described in a very negative manner. The aspect of personal anger is not involved.
Vengeance is an act of restoring wholeness to the community.
The avengers were not acting in their own behalf but in behalf of the family or community as an instrument of God. This segment of the priestly regulations seeks to modify that rigidity. Hill, Andrew E. and John H. Walton. A Survey of the Old Testament. Jensen, Irving L. Jensen's Survey of the Old Testament.