The Appeal: Many cops are idealists: They feel they're there to uphold the law and safeguard innocent citizens, one reason the uniform carries authority. And since it's government work, job security is usually good.
The Reality: Police work is stressful and dangerous, especially in high-crime areas. On the street, cops often feel they're doing little more than keeping a lid on problems that are far bigger than they can control. Police officers also do a surprising amount of paperwork; every intervention must be carefully documented. And that discourages a lot of cops—they're people of action, not of copies in triplicate.
Alternative: Homeland Security official. Many experts think terrorist threats to the United States are likely to increase, with scenarios that could involve poisoned water supplies, communicable viruses released in subways, or nuclear bombs in backpacks. People motivated to protect the citizenry can find plenty to fulfill them.