Is a person considered insincere in his intention if he abandons forbidden acts, such as looking at what is unlawful and committing adultery, because he would not accept them for his sister or mother, and because they are forbidden?

A servant's abandonment of sin because it is forbidden is the essence of sincerity, and it does not contradict his dislike of it for his family and relatives. The hadith (definition) of the young man who sought permission to commit zina (fornication/adultery) indicates that a person's dislike of forbidden acts for his family is not blameworthy. The Prophet, peace and blessings be upon him, convinced him that what he would not like for his mother, daughter, sister, paternal aunt, or maternal aunt, people also would not like for their relatives.