[1] Although Moll was a pioneer of sexology, his contemporaries such as Magnus Hirschfeld and Sigmund Freud eclipsed his work, primarily due to the bitter rivalry between them.
[3] Born in Lissa (then part of Prussia) to a Jewish tradesman, Moll attended Catholic school in the Silesian city of Glogau before studying medicine in Breslau, Freiburg, Jena, and Berlin.
[4] On a tour of Salpêtrière Hospital in Paris, Moll observed the now-famous demonstrations of hysteria and hypnosis by Jean-Martin Charcot.
[1] Moll's publication Das Sexualleben des Kindes (1908) enraged Sigmund Freud for its criticism of psychoanalysis.
Moll remained unconvinced of Freud's case studies, suggesting the symbolic representations he made were guided only by his assumptions and not empirical evidence, meaning they had no scientific use in determining the theory's soundness.
Moll regarded himself as a pure scientist free of political interests while Hirschfeld identified less with the medical profession and more as a scientific humanitarian.
In his letter, Moll claimed that Hirschfeld's reputation as a physician and scientist was marred by his politics and personal convictions.
He went on to describe Hirschfeld as a "duplicitous opportunist", portraying himself as a militarist until his political associations were unveiled on the day of the revolution in Berlin.
His own reflections and comments on those studies were considered to be much more in depth than some other sexologists of the time, including Krafft-Ebing whom Moll admired (as a matter of fact, he completely revised and updated his famous Psychopathia sexualis, issuing in 1924 its 16th-17th edition).
[10] In the 1920s, a shift in German public opinion led to harsher punishment of sexual crimes despite no changes to the law.
German sexologists and medical psychologists, often called as expert witnesses in such cases, responded with a petition for the legal equivalence of homosexual and heterosexual acts between consenting adults.
Moll claimed that self-guilt or abhorrence were negligible from a medical point of view, as was the question of homosexual heredity.
Moll opposed harsh legal penalties for consensual homosexual acts while also promoting conversion therapy, a practice now considered harmful.
Numerous sexual drives and actions, including masturbation, attraction to those of the same sex or different ages, and other fetishistic inclinations, were not uncommon in childhood and did not necessarily indicate the development of perversion in adulthood.
Moll argued that psychological and environmental triggers preventing the natural transformation of infantile sexual urges are the determinants of perversion.
[16] Moll was a member of a group of doctors in West Berlin that treated different psychological illnesses using hypnotism, focusing on addiction and sexual ailments—including homosexuality, which was considered a perversion at the time.
In the book, Moll criticized practices such as Christian Science, spiritualism, and occultism, claiming they were the result of fraud and hypnotic suggestion.
He argued that suggestion explained the cures of Christian Science and the apparently supernatural rapport between magnetisers and their somnambulists.
According Heather Wolffram, "[Moll] argued that the hypnotic atmosphere of the darkened séance room and the suggestive effect of the experimenters' social and scientific prestige could be used to explain why seemingly rational people vouchsafed occult phenomena.
"[17] In 1903, Moll tested Clever Hans and was the first to suggest the horse was not psychically gifted but was reacting to unconscious signs.