Why is the love between brother and sister, the love between father and daughter, and the love between mother and child taboo now? What are the reasons for the taboo?

From the biological point of view, the combination of close relatives is very unfavorable to future generations, with a high rate of disability and deformity, and even spontaneous abortion, which is the survival of the fittest for human beings; From the perspective of social ethics, this is incest, and it has to bear great pressure from public opinion; From a literary point of view, labeling forbidden love is a gimmick.