JOEL - Why did God kill all those people in the flood? Why did God kill all those people in Sodom and Gommorah? Why did God kill all of Pharoah's soldiers when Noah crossed the Red Sea? Moses himself, descending from Sinai’s summit with the Ten Commandments as fresh in his mind as they were in his hands, immediately caused 3,000 Israelite idolators to be slain. Why did God allow Jesus to suffer and be killed on the cross?
The key point in all these incidents, including the case of Laban, is that it was God's decision to cause the death of someone for His greater purpose. We can't begin to understand why God does things in a certain way.
"For my thoughts are not your thoughts, neither are your ways my ways, saith the LORD." (Isa 55:8)
The incident with Laban may well have been a trial of faith for Nephi. The Lord could have helped him procure the record in some other way. Instead, the Lord allowed Nephi to struggle with a dilemma: obtain and safeguard the plates as he had been commanded, or let Laban live.
The Ten commandments are God's commandments on how man is to treat God and other men. Whatever God decides to do will never be limited by the earthly commandments He gives to His children on earth.
Our scriptures tell us that God "willeth to take even them whom he will take, and preserveth in life them whom he will preserve;" (D&C 63:3)
In God's judgment it was necessary for Laban to be removed so that an entire future nation would not dwindle in unbelief(1 Nep. 4:13). Because the brass plates were obtained and made available to the Nephites, they were able to preserve the revelatons and prophesies that allowed them to learn and believe in Jesus Christ and prepare for His coming. Without those brass plates we might not even have the Book of Mormon.