While it's easy to get caught up in Herod Sayle's evil genius shtick, we come to realize that there's a real human being with real feelings underneath. This certainly doesn't justify Sayle's actions, but they certainly place them in a different light.
At first, Sayle seems little more than a Dr. Evil-style villain. Think back to how Sayle acts with Alex when he first arrives, telling the fourteen-year-old that being killed by his "awesome and repulsive" jellyfish would be an "unforgettable death" (7.25, 7.32). At the time, Sayle thinks Alex is Felix Lester, a kid who won Sayle Enterprises' equivalent to a Golden Ticket. What kind of whacko would act like that to a kid who won a contest for a free tour of his facility? Egads.
It's not until his final big monologue that Sayle reveals that childhood bullying—yes, you read that right—is what motivated his plan for revenge. Born in the slums of Egypt, Sayle was adopted by English parents and brought to what he considered to be the "heart of civilization (13.25). Although he loved England at first, he "came to hate it" in "only weeks" (13.27), after being tormented with racially and class-based bullying.
Of course, Sayle doesn't react to this bullying in the right way by any stretch of the imagination. But, like all great evil masterminds, Sayle is a sympathetic character whose original innocence was demolished and rebuilt into something nasty. We're sure that in the rest of his life Alex—a handsome, athletic, intelligent, and charismatic young man—doesn't have to deal with bullying anywhere near the level of Sayle. Still, nothing justifies the twisted path that Sayle chooses to walk down.