We have before said that when we do not find persons at home, or when we are afraid of disturbing them, we leave a card; but this is not what we call particularly visits by card (visites par cartes.) In these last visits, it is not our object to see the persons, since we do not ask for them, and we confine ourselves to giving our card to the porter or domestic. This custom, which has been introduced necessarily among persons of very general acquaintance, and especially at times when every one ought to be visited, as on the new year's day, is not considered ridiculous; but it becomes so by the great extent which has been given to it for some time past. This extent consists in making a visit without leaving our apartment; that is to say, merely by sending our card by a domestic, or indeed by means of an agency established for this purpose. The practice of visits by cards, seems to persons of good society the most impertinent and vulgar thing which can be imagined.
--From The Gentleman and Lady's Book of Politeness and Propriety of Deportment--
Some people send out greeting cards thinking they are keeping a nice tradition alive; but traditionally, business cards were the only cards given out, and almost always in person.
What was considered especially vulgar was leaving out cards other people gave you.
Take that Hallmark!