What did okonwko do to Ikemefuna? and why?

In Chapter Six, Okonkwo is enjoying locust when Ogbuefi Ezeudu enters. He is a great village elder, and he has come to inform Okonkwo that the time has come for Ikemefuna's death. They tell Okonkwo not to bear a hand in the child's execution. The next day, a large group of elders comes to Okonkwo to discuss it more fully with him. Later that day, Okonkwo tells Ikemefuna that he is to be sent home. Nwoye hears, and begins to cry; his father beats him heavily.

A group of men brings Ikemefuna deep into the forest. The boy thinks about how strange it will be to see his family again; he is excited to see them, but also said to be leaving his new family. They walk for hours. The other men attack Ikemefuna with hatchets. He runs to Okonkwo, calling him father, begging for help. Afraid of being thought weak, and full of a terrible fear, Okonkwo uses his matchet to strike the boy down. Okonkwo kills the boy for the same reason he makes most decisions in his life.... he doesn't want to be perceived as weak.