Aleksandr Solzhenitsyn helped me to understand how things like this can happen.

“... the line separating good and evil passes not through states, nor between classes, nor between political parties either -- but right through every human heart -- and through all human hearts. This line shifts. Inside us, it oscillates with the years. And even within hearts overwhelmed by evil, one small bridgehead of good is retained. And even in the best of all hearts, there remains ... an un-uprooted small corner of evil".

This quote is taken from his book The Gulag Archipelago. I can recommend it if you are looking for answers.