Hypnotism, therefore, is a dangerous, if not a morally detestable, practice. In the process of suggestion the individual alienates his liberty and his reason, handing himself over to the domination of another. Now, no one has any right thus to abdicate the rights of his conscience to renounce the duty towards his personality. It has been objected to this view that there is the same effect in intoxication or in the use of chloroform; but the argument is of no validity. Drunkenness is not justifiable; it is a grave sin against temperance. As for chloroform, it has its precise indications strictly marked. It is only lawfully employed in medicine to make insensible sick people who are about to undergo a surgical operation. Can hypnotism be employed in the same way as chloroform? Has it any social utility, or does it play a humanitarian rôle in any way? Its supporters have vainly endeavored to endow it with practical uses, in order to give it a scientific turn, but in spite of all their efforts, hypnotism remains, not only an idle curiosity, but a dangerous game. Such is the certain conclusion to which we are led by a study of hypnotism in its relation to civil and criminal law. It is a generally recognized fact that criminal or unlawful acts have been, or can be, committed on sleeping subjects. Even without proceeding to actual crime, the hypnotist may make insidious and improper suggestions. Many have boasted of having obtained delicate secrets from young girls, humiliating avowals which they certainly would not have made had they been awake; such procedure is an odious abuse of confidence. We pass on to the consideration of crimes due to hypnosis: women have been made the victims of attempts on their honour, and even of actual rape. Sometimes, too, by means of suggestion, the subject is made to consent to the crime, as criminal records show. We have no properly ascertained cases of fraud or theft successfully practised by means of hypnosis, but such things are nevertheless possible. The evidence given in all such cases should be regarded with mistrust; the subject may be deliberately trying to deceive, or he may be in good faith mistaken, and so accuse an innocent person. Of this the famous La Roncière case (1834) is a sad illustration
This comes from the Catholic Encyclopedia website.