Assuming that the advent of the internet has actually increased the chances of sexual deviance and sex crimes, it is because of two things. First, it is because of greater access to sexualized content and second, it is because of greater ease of contacting possible victims.
It is possible that more people come to have deviant sexual desires since the internet has been widespread. If this is true, it is likely because people have more access to sexual images on the internet. It is very easy today to find sexual images of all sorts on the internet. These could help to develop deviant sexual urges that might previously have remained rather dormant in the individuals.
It is certain that it is easier to come into contact with people today with the prevalence of the internet. People with sexually deviant feelings can stalk potential victims on things like social networking sites. They can find potential victims much more easily than they once would have been able to do. They are more likely to be able to strike up relationships with these victims online than they would be able to in person. They can then sometimes persuade the victims to meet them in real life.
Thus, the internet may make it more likely that people will form sexually deviant urges and it definitely makes it easier for people to come into contact with potential victims.