The sex drive is the strongest drive in an animal, isn't it? Besides maybe protecting offspring and self-preservation. So maybe #3. Well, imagine being the poor sucker whose genes tell him to be attracted mainly to kids.
That being said, the conscience should prevent them from acting much on that instinct because they should know that it's damaging to children and deeply upsetting to parents.
It's my personal suspicion that pedophiles who actively molest children are actually a combination of pedophile and sociopath.
However, to some degree they are probably also rationalizing desperately in order to be able to fulfill their basic instincts. Humans are remarkably good at rationalizing behaviors that come from deep-seated needs. So it could be that the inner conflict between conscience and pedophiliac instinct sometimes results in a deadening of the conscience, in effect making someone who was not born with sociopathy into a functionally sociopathic person.