At the risk of Godwining this thread, Hitler was really, really convinced that Jews were evil schemers that dealt in betrayal, fraud and conspiracy against innocent and naive Gentiles. And that their destruction was a necessary step to cleanse the Earth off their evil.
It goes back even further, actually, and provides another data-point for this aphorism. The Teutonic Order, a sort of ... indirect relative/precursor [0] to the German Empire/Republic which the Nazis grew in was notorious for doing some really horrific things in the name of God, and in trying to force convert the lands north of Prussia/Poland. The surrounding Christians states didn't really approve of this, and eventually pushed them back. They seemed to be pretty obsessed themselves with the idea that other Christians were backstabbing and betraying their cause.
It seems their cause was, originally, in good intentions. I'll give them the benefit of the doubt at least. But it's clear by the end they fulfilled this aphorism, and became a great evil by trying to fight evil.
[0] The Teutonic Order held land, the "Deutschordensstaat". When Martin Luther convinced the then-Grand-Master Albert to convert, he turned that land into a secular state, the Duchy of Prussia, which became the Kingdom of Prussia, which became the leading state of the German Empire.
Carpet bombing of German cities was, in hindsight, probably not just evil but militarily inefficient. The official goal - to disrupt industrial production - was never really achieved.
The end result: Auschwitz.