A friend sent me this quote, he said I asked him about it two years ago. I don't remember asking, but I'm grateful he sent it.
"Henceforward the Immaculate Conception became an apple of discord between rival schools of Thomists and Scotists, and the rival orders of the Dominicans and Franciscans. They charged each other with heresy, and even with mortal sin for holding the one view or the other. Visions, marvelous fictions, weeping pictures of Mary, and letters from heaven were called in to help the argument for or against a fact which no human being, not even Mary herself, can know without a divine revelation. Four Dominicans, who were discovered in a pious fraud against the Franciscan doctrine, were burned, by order of a papal court, in Berne, on the eve of the Reformation. The Swedish prophetess, St. Birgitte, was assured in a vision by the Mother of God that she was conceived without sin; while St. Catharine of Siena prophesied for the Dominicans that Mary was sanctified in the third hour after her conception. So near came the contending parties that the difference, though very important as a question of principle, was practically narrowed down to a question of a few hours. The Franciscan view gradually gained ground. The University of Paris, the Spanish nation, and the Council of Basle (1439) favored it. Pope Sixtus IV., himself a Franciscan, gave his sanction and blessing to the festival of the Immaculate Conception, but threatened with excommunication all those of both parties who branded the one or the other doctrine as a heresy and mortal sin, since the Roman Church had not yet decided the question (1476 and 1483)." [Source]