What is the psychology behind paedophilia?

Please do not respond to this question if you just want to slag off paedophiles

I want to know the processes behind this. I truly believe we are all born ‘good’ and I think something happens to people that makes them this way

Are there different levels to this ‘disease’?
Is it black and white?
What has happened to these people to make them this way?
Does thinking about it make you a paedophile or do you have to act upon it?