If society didn't exist, maybe. But in real, functioning societies, people care about their standing, and being seen as a fraudster is not a positive outcome. If "being seen as a fraud and outcast for life" is a possible outcome, people in normal societies don't give that risk zero value. So it doesn't always require actually imprisoning someone to deter behavior. Keeping someone locked up in a cage is a pretty extreme sanction, both expensive and odious and best reserved for really rare cases where there is no other alternative. Usually that means violent crimes with no reasonable prospect of releasing the perpetrator without recidivism, in which case imprisonment is a last resort to protect society—Breivik type cases. Beyond that, imprisoning someone is prima facie evidence of failure, a knee-jerk reaction to not being able to run a financial (or other) system properly.