This one.
In fact, only in modern times have women dreamt of going to university, but the idea has now become so normal that even Catholics, whose Faith guards Nature, may have difficulty in seeing the problem. However, here is a pointer in the direction of normalcy: any Catholic with the least respect for Tradition recognizes that women should not be priests - can he deny that if few women went to university, almost none would wish to be priests? Alas, women going to university is part of the whole massive onslaught on God's Nature which characterizes our times. That girls should not be in universities flows from the nature of universities and from the nature of girls: true universities are for ideas, ideas are not for true girls, so true universities are not for true girls. (Bishop Richard Williamson, SSPX)
Perhaps they believed that the Pope and other Bishops were antichrists, as Lefebvre had wildly accused in 1987 to his Bishops-to-be?