The dissent against the medieval order was in 1517 already a millenium old and extremely widespread. Because it had been obliged to carry on under cover, so that conference between the dissidents was quite out of the question, it had gone in all directions. The “medieval underground,” as it has been called, was unable to have its “town meetings” to discuss and then come to consensus; hence the endless variety. The Church called all its foes by one and the same name, “heretics,” who “like the foxes of Samson, have diverse faces but are all tied together at the tail.” The Church had no desire to differentiate between group and group; they were all guilty of one and the same sin, that of challenging her monopoly; and she vented her spleen on them indiscriminately.
This will go far to explain why the “Left-wing of the Reformation” or the “Radical Reformation,” or whatever one wishes to call the camp that developed the Second Front, shows such bewildering diversity. The Church had long had a sort of catch-all, a kind of wastebasket into which she thrust everything she didn’t want; when the Reformation failed to satisfy there was again and at once the same multifariousness; Menno and Muntzer, Schwenkfeld and Servetus, and many more, all clubbed together under a single label.
Fortunately for us, the record shows that there were great polarities right within the camp of the “heretics,” in medieval times and also in the days of the Reformation.
Leonard Verduin, The Reformers and Their Stepchildren (Sarasota: Christian Hymnary Publishers, 1991. p. 15.)
One Pilgrim's Progress 