(a) Hence, the greater the sin that will be committed or the more harmful the consequences that will ensue from the use of an object, the greater the reason required for making, repairing or selling it. In some instances only a most grave reason will excuse, such as peril of instant death for refusal. Thus, one may not sell poison or drugs to a person who contemplates suicide, murder, or abortion. One may not sell narcotics to a person who asks for them in good faith and who cannot obtain them elsewhere, but who will become a drug-fiend if they are given him. One may not sell morphine, heroin, etc., to a person who is already a drug-addict and who will abuse the drugs, unless there is a very grave reason for not refusing, such as danger that refusal will lead him to set fire to the building. If one has all the playing cards in some remote hamlet, one should not sell them without grave reason to a customer who will spend a great part of the time at games to the neglect of serious duties, nor without a very grave reason to a customer who is a card sharper and who will swindle many innocent victims, or to a gambler who will waste the money due to his wife and family.
(b) The more closely related an object is with sinful uses, the graver must be the excuse for having part in its manufacture or sale. Thus, an ordinary reason (e.g., profit) might suffice for selling a lamb to a pagan or attractive ornaments of dress to a woman, where only a very grave or most grave reason would suffice for selling incense to a pagan or ornaments that are frequently used as amulets or charms. Generally speaking, it is seriously wrong and gravely sinful to make or sell articles whose ordinary use is gravely sinful.
(c) The more a customer depends on a determinate manufacturer or merchant to obtain such an object, the more serious must be the reason for making or selling it. Thus, a grave reason, such as a notable loss, is sufficient reason for selling a special fancy apparel to a notorious “vampire” (i.e., a woman who carries on scandalous flirtations in order to get presents), if the adornments can be obtained from other dressmakers or modistes or stores; but a much graver reason would be required, if the apparel could not be purchased except at one place. In the former case, refusal to sell would not prevent the activities of this woman; in the latter case, it would at least hinder her to some extent.
(d) The more certain it is that an object will be employed sinfully, the greater must be the reason for making, repairing or selling it. Examples: Sempronius, a curio dealer, is asked by three men for a statue of Joss along with joss-sticks and papers. The first customer says he intends to use these articles for religious rites; the second will not tell what his purpose is; the third wishes to present the articles to a museum. Sempronius may not sell to the first customer except for a most grave reason, such as fear of death if he refuses; he may not sell to the second customer without a very great reason, such as a very considerable loss to himself; he may sell to the third customer for an ordinary reason, such as the profit he makes from the sale. Titus, who sells firearms, knows that some of his customers, though he has no particular individuals in mind, will use these weapons unlawfully in poaching or shooting out of season. Since evil is not to be presumed of any particular individual, Titus has the right to sell to all for the usual reason of business profit.
1536. Is a merchant bound to inquire the use which a customer will make of an article that is often employed for sin?
(a) If the positive law requires that the merchant inform himself, he is bound to make inquiries necessary for obtaining the information. Thus, if the civil law forbids the sale of weapons without a permit or of poisons without a prescription, the merchant has to ask for the customer’s authorization to buy.
(b) If the positive law has no such regulation, we should distinguish between articles that are frequently used for sin and articles that are generally used for sin. When an article of the former class is requested, there is no obligation to make inquiries, for such an obligation would be unduly burdensome; but, if an article of the latter class is desired, one should make inquiries, unless one is morally certain that the intention of the customer is good, or there is a very grave reason for seeking no information. Thus, one may sell a deck of cards to a stranger without asking for proofs that he is not a confidence man in disguise; but one may not sell deadly poison to an entire stranger merely on the strength of his word that he needs it for medical or other lawful purposes.
1537. Sinful Cooperation in Providers of Food and Drink.—(a) There is explicit formal cooperation with sins of gluttony, drunkenness, violation of fast or abstinence, whenever one gladly supplies the means for these sins to those who are about to commit them. Thus, if a host supplies a guest who is overdrinking with all the intoxicants the latter desires, and secretly wishes that the guest may make himself drunk, there is explicit cooperation. There is implicit formal cooperation when he who supplies the food or drink does not directly intend evil, but when the act of giving the food or drink is from the circumstances of the case an evil act, as when a person is given a meal which will not agree with him and will make him sick or aggravate a malady, or when a person who wishes to violate a fast ostentatiously to show contempt is furnished with the eatables he asks for. (b) There is unlawful material cooperation when one does not approve of the sin that will be committed, but nevertheless without sufficient reason supplies the food or drink. Thus, there is sinful cooperation when a restaurant owner gives meat on Friday to one not dispensed, for no other reason than the profit he himself will make.
1538. Material cooperation in providing food or drink to those who ask it, but have no right to take it, is lawful when one has the right to provide the food or drink, and there is a sufficient reason for cooperation. The sufficiency of the reason depends on circumstances, as explained in 1519.
(a) Hence, a greater reason is required when the sin that the other person will commit will be greater. Thus, a grave reason, such as indignation of a customer, might suffice for cooperation with a venial violation of temperance or abstinence; but a graver reason, such as a serious quarrel, is required if the violation will be mortally sinful. A graver reason is also necessary when the consequences will be more harmful (e.g., the fights of the drunkard, or the serious illness of one who has neglected his diet) than when they are less harmful (e.g., the foolish talk of the drunkard, or the stupefaction of the glutton).