When asked about his charity work he talked about a "ledger" where the "good" would be made to "counterbalance" the "bad" when he was before St Peter or God. He seemed to think like this.
To some extent, we all think a bit like this. I recently went through a speed trap on my motorbike. I was slightly over the 60 mph speed limit on a dry empty road in broad daylight. I remember feeling aggrieved because I am always scrupulous about 30 mph limits. I felt that my unusual degree of compliance in one area ought to "offset" my minor infringement in another. (As it happens, no ticket arrived, so I must have been within the wiggle room the police allow.)
In the context of religion, it is easy to find examples of believers attaching enormous importance to one thing in their chosen book (e.g. homosexuality being forbidden) but you seldom find religious groups protesting at a sea food stall because it is selling shellfish, or waving banners outside farms where mixed breed cattle are kept.
"Show me what you find in your Bible and I will know you better."
Taking this form flimsy rationalisation as a norm of human behaviour, it is easy to see how someone whose behaviour is far outside the norm might rationalise in an extreme and absurd manner as has been suggested about Savile.
No one can help the urges they feel (I feel an urge almost every day to tell my customers what I really think) but someone who acts on urges that have appalling life-changing consequences for other people (such as a child molester) is either incredibly wicked, or mad, or both. That will affect all aspects of their thinking.
I wonder to what extent Savile's Roman Catholic upbringing made him feel guilt and shame, somewhere in the back of his mind. The RC upbringing embeds ideas of guilt and penance. (As Dara O'Briain says, "I'm an atheist, but I'm still a Catholic.")
In Roman Catholicism, there is a long history of rationalisation about sin and penance. Jesus may have neglected to mention it, but there is the concept of purgatory. In medieval times, the living could buy indulgences: pay money to the church to shorten the time in purgatory for family members who had already died.
For someone like Savile, who clearly had the disposition to pick and choose which parts of his childhood faith did or did not apply to him, it is easy to see how he could construct a rationalisation that involved him paying a fair price to be forgiven for his sins.
I'm not religious myself, but my understanding of the Christian faith is that God will forgive sins if the person truly repents. It is quite clear that repentance was not in Savile's mindset.