In other words, the incest taboo was adopted to assure peace within the family circle, a convenience measure dictated by jealousy.
Repressed Incestuous Feelings may at times drive one into a most objectional form of behavior. A brother who in childhood was too fond of his sister (or vice versa) may, from an unconscious desire for self-protection, adopt a hostile attitude to his sister. The more attracted he was to her the more sadistic he will appear in later years.
He may even avoid all the women who would in any way suggest his sister and in that way never feel satisfied in love, for the women who cannot possibly suggest to him his sister, lack all the fetishes which would vouchsafe him safety and eroticism.
Such a man should be analysed and made to realise the incestuous cravings which he has repressed into his unconscious. His hatred would then change into affection and in his search of a mate he would logically seek the sister image which alone would insure him sexual happiness.
I have reconciled in that way several groups of brothers and sisters who had never been able to get along after puberty, altho most of them had developed a dangerous fondness for each other before puberty.
Repressed sister fixation like repressed mother fixation has been found on several occasions as one of the components of homosexualism in the man, father or brother fixation as one of the causes of frigidity in the woman.
Blood Relations. Mother or sister fixation is frequently the cause of marriage between blood relations. This sort of union has been unjustly suspected of breeding mental inferiors. We should rather say that it is the mental inferiors who seek their mate within the family circle. Unable to secure the mother or the sister as a mate, they select a woman who has as many of the family traits as possible, that they may feel more secure in her company. If a defective child is bred of such unions, it is not due to the close relationship of the parents but to the fact that too often one of the mates was deficient physically or mentally.
In this respect as in many others, self-knowledge and acceptance of one's personality, coupled with a courageous understanding of unavoidable biological facts, are the necessary conditions for perfect mental health and freedom.
The man with a mother or sister fixation, the woman with a father or brother fixation should be made aware of it, however slight or severe the fixation may be.