There is also the legal aspect. Christ was not on earth to serve as a judge in criminal or civil matters, which he stated clearly in Luke:
13 Someone in the crowd said to Him, "Teacher, tell my brother to divide the family inheritance with me." 14 But He said to him, "Man, who appointed Me a judge or arbitrator over you?" (Luke 12:13-14, NASB)Jesus knew that in bringing the woman to him (without her male partner, as required by law), his adversaries were not interested in justice for this woman’s husband, but rather in ensnaring Jesus in a dilemma. Jesus first dealt with the accusers (by his mysterious writing in the sand) and then closed the story on the legal farce by sending the woman away—with the admonition to cease her sinful ways.
Adultery may no longer be a crime punishable by death, except for women living under the Religion of Peace, but what about other heinous crimes, such as murder?
Paul makes what I consider a straightforward statement that God has given the right to civil authorities to administer capital punishment:
3 For rulers are not a cause of fear for good behavior, but for evil. Do you want to have no fear of authority? Do what is good and you will have praise from the same; 4 for it is a minister of God to you for good. But if you do what is evil, be afraid; for it does not bear the sword for nothing; for it is a minister of God, an avenger who brings wrath on the one who practices evil. (Rom. 13:1-4, NASB)It seems to me that bearing the sword as a minister of God in order to bring wrath to one who practices evil is a clear description of the legality of capital punishment.