From Ignatius Insight:

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It is an explosive and ultimately uncontrollable force that can destabilize and undermine church and government. It can reject time-honored truths, traditions and institutions—including its own—and posit new ones in their place, only to repeat this process again and again. Protestantism is infinitely restless, constantly moving in many divergent directions at the same time. Like evolution, it possesses astonishing power to create highly adaptive religious organisms and equally astonishing power to destroy them if they fail to develop appropriately.

No, that isn't from a Catholic apologist; it is from Ronald K. Rittgers, who teaches German Reformation studies at Valparaiso University in Indiana, in his review, for The Christian Century, of Alister McGrath's recently published Christianity's Dangerous Idea: The Protestant Revolution—A History from the Sixteenth Century to the Twenty-First:

This is how Alister McGrath, professor of historical theology at the University of Oxford, depicts Protestantism in Christianity's Dangerous Idea. Why is Protestantism so dangerous? Because it is based on a dangerous idea: that the Bible is the main source of authority for the Christian religion and that all Christians have the right to interpret it for themselves. This conviction is the source not only of Protestantism's vitality and flexibility, but also of its lack of fixedness and its innate tendency toward schism. McGrath makes much of the former without losing sight of the latter.

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McGrath also stresses that early Protestantism was not a single, unified, coherent movement; it was a movement of movements that was characterized by conflict, tension and flux from the start. The only thing the early Protestants shared was the dangerous idea. And they quickly learned just how dangerous it could be when they found themselves unable to reach consensus on important matters of doctrine. After examining the failure of Luther, Zwingli and others to resolve their differences on the Lord's Supper, McGrath observes, "We see here the fundamental difficulty that the Reformation faced: the absence of any authoritative interpreter of scripture that could give rulings on contested matters of biblical interpretation."

More at this link.