True, but they are usually high functioning, which means they can appear to be completely normal to the average person. They are usually well liked by other people which is why they are the least suspected people in your community.
For example, most children are targeted by people they know such as a relative or family friend.
These pedophiles usually work very closely with children in various settings such as church, school, sports teams, etc. This doesn't mean that everyone that works with children is perverted, but it does tell you how stealthy pedophiles can be.
Not ALL sex offenders are screwed up in the head. I know a guy that had to register as a sex offender for indecent exposure in public only because he got caught peeing in the bushes late at night. He had no intentions of any sort of sexual activity. He just needed to pee and there was no public restroom available at that time of night, so he did what millions of other men have done for millions of years - he peed in the bushes. Now, he tells other males, "DO NOT PEE IN THE BUSHES!"