Catfish is correct in his listing that a lack of true empathy is a hallmark of sexual abusers. The kinds of mental gymnastics many use to justify the abuse is evident in their explanations (in some, not all or even most cases) that they are trying to make the victim "feel good".
This is especially evident with those who target pre-pubescent boys who (as Mellifer accurately points out) are in the PROCESS of puberty. It is not an event but a process. The event for a girl will be the day she gets her period; for the boy, his first ejaculation. However, the pubertal process is taking place for months prior to these events.
These indiduals will sometimes abuse the boy with masturbation or oral sex to "make him feel good" as he is experiencing the sexual feelings that come into greater focus at this time. The ability for prepubescent children to experience sexual arousal and feelings from stimulation takes place in the womb and then onward. In normal (i.e., non-abusive, self stimulatory) situations, they may experience orgasms from the stimulation. Or, when someone stimulates their bodies to the point of orgasm, they generally don't know what is going on.
This is insidious in terms of how the child/young teen experiences the feelings and the relationship with the abuser. It is often at the heart of the confusion (including sexual identity) that he experiences. The lack of empathy was exemplified by a 16-year old boy I worked with in a residential treatment program I was at years ago.
When talking about performing oral sex on an 8 yr old boy, he told the group that he used empathy in his offense and thought at the time, "Who doesn't enjoy getting a blow job?" From his perspective (as a sexually mature teenager), the idea of receiving oral sex was perfectly fine. As the other boys in group pointed out to him, the 8 yr old doesn't understand the context and experiences confusion around the pleasurable feelings and this teen was lacking the empathy for the child and his developmental level.
So, empathy is generally lacking. Afterall, anyone who experienced sexual abuse or believed that he was doing something beneficial for the victim is just not there.