Do you really believe that these guys are just looking to get laid? Bullying can start at a very early age: 5, 6, 7, etc. It's victims can endure years of ego crushing abuse. It can come from parents, siblings, other school children, teachers, coaches, religious, or anyone in some level of authority. Their choice is the most vulnerable.
These guys are looking for love and validation, not just sex. when they get enough nerve to reach out and are repeatedly rejected, they despair and seek to punish others for their misery. Nonetheless, they are responsible for their actions.