Thomas Haden Church says Flint (Sandman) Marko is a complex character with motivations that transcend mere personal profit (e.g., robbing banks).
"I can't be specific about what it is, but I will say that he's definitely a guy who has a purpose in the movie, and that purpose is absolutely in conflict with Spider-Man's better intentions," the actor told Superhero Hype. "I wouldn't be a villain in the movie if it were otherwise."
"[T]here are some larger life issues at play. He's really got a lot of stuff to work out and like I said, it's not in Spider-Man's best interest," Haden Church said.
You can read the rest of the interview here.