Blessed John Duns Scotus & Unintended Consequences
John Duns Scotus was one of the leading theologians of the late medieval period (he lived from 1265-1308). Unfortunately for him, his name is the origin of the modern word "dunce", indicating someone who ain't to keen. In fact, he is known as the "Subtle Doctor" for the rigor of his intellectual work. He was the thinker who developed an explanation for Mary's Immaculate Conception which was later ratified ex cathedra when Pope Pius IX defined that Marian doctrine, and Scotus was also renowned during his own lifetime for his holiness: virtully immediately upon his death, he was referred to as "blessed" (his official canonization wouldn't come for quite some time: JPII beatified him in 1992!).
Having said that, I've found over the last several years that we've got the good doctor to thank for all sorts of problems in theology (and hence, elsewhere). For instance...
First, in research for my dissertation, I found that while Ockham is rightly criticized for positions on sin and grace which Luther would rightly reject (erroneously believing that they articulated authentic Catholicism), many of Ockham's problematic positions could be traced at least in part to Scotus' own thinking.
More recently, I've found scholars who argue that criticisms of virtue ethics trace themselves beyond Kant and Ockham to Scotus and his division of the will.
Finally and also recently, I've found that the theological "tendency" called Radical Orthodoxy sees Scotus' metaphysics as the harbinger of modernity and its attendent secularism.
Now, I think it's clear that we're talking about unintended consequences here; Scotus was a faithful son of the Church, a holy man, and a brilliant thinker. But some of his thoughts turned out to have conclusions which were and are detrimental to Catholic Christian thought and practice.