"You" should? Who is "you"? Just any guy on the street who decides someone else is wrong?
I am afraid that people toting this canard are seriously misinformed about the nature of Sacred Scripture, and Moses' role in leading the Israelites at that point in time.
For the Israelites, and the Jews living in Israel, Moses' law was the law of the land, the law ordained by God. It wasn't vigilante justice or extrajudicial killing. It wasn't no angry mob picking up rocks to stone someone they didn't like.
The stoning of guilty parties that was prescribed, was a state-level execution. It would be the same as any criminal who undergoes arrest, trial by peers, conviction and sentencing.
So if Kirk was saying that God's law prescribed some sentence for some offense, I hope that we can agree that Kirk wasn't encouraging gun-toting vigilantes to go out lynching people in the night without due process or without actual legislation.
Furthermore, we also need to consider the context of these citations in the course of a debate process. Kirk was not a deranged pastor shouting for violence from his bully pulpit. Indeed, many of the debates found him confronting students who were deranged or deluded in many ways, and Kirk would never shy away from meeting them where they were at.