The correct answer to this open question is the following.
The family members in The Metamorphosis justify their decision to get rid of the insect in that they convince themselves that the insect is not Gregor.
We are talking about the novel "The Metamorphosis," written by Franz Kafka in 1915. It is a story of a man named Gregor Samsa that wakes up one morning transformed into a big insect. This impacted his family so much and he has to adjust his life to this new condition. Gregor tries to maintain his normal routine of life, work, and family relationships.