Power
You have the power to grant or deny people access to this country, which can have a major impact on many lives. You're America's gatekeeper. Don't underestimate the power that this position brings.
People don't necessarily get into this position because it makes them feel powerful—standing at a kiosk and asking a bunch of smelly, rumpled travelers the same questions all day generally doesn’t make you feel like James Bond—but you've still got power in spades. You may end up testifying in court on behalf of an immigration case or be responsible for the actual detaining of people in violation of immigration laws.
You've got a lot of power over a lot of people's lives. Make sure to use it wisely.
Working for the federal government means working directly under the people who control a lot of this country's rules. As a low-ranking inspector, you won't have much say in those rules. If you do feel strongly about immigration laws, your best bet would be to make sure you work hard to get promoted so you have more of a say in the decision-making.