It is easy for people to abuse authority when they want to - decide to - abuse authority. But further, such cases are not an "abuse of authority." They are an abuse of a human being. And quite honestly, having been in such positions of authority with vulnerable human beings, I cannot - internally - conceive of such a desire.
Lord Acton of course famously said, "Power corrupts and absolute power corrupts absolutely." But the Anglo-Saxons had a slightly different take, expressed in the maxim: Man de■ swa he by■ ■onne he mot swa he wile.
"A man does as he is, when he may do as he wills."