If you love someone, don't EVER support their desire to become a cop.
They may have been a good person before they became a cop, but they can't be good once they are a cop. A cop in the family is nothing to be proud of-- almost anything else (including a crackhead or a $5 hooker) is better.
You might actually believe your son or your niece is too good a person to become a vile murderer just because they become a cop. Before they become a cop you're probably right. They probably have the best intentions. They may really want to help people, and may not realize that every cent they are paid as a cop is stolen from others.
The problem is, ignoring the stolen money, the "police culture" will make them come to believe they aren't doing wrong no matter what evil they participate in. It's a ratcheting effect-- each little act of law enforcement they commit will make it easier to commit the next. And it will make it easier and easier to commit slightly worse acts of enforcement. Every traffic ticket issued will bring them closer to murdering a person for not complying with a nonsensical demand fast enough. Each "property code" excuse to rob someone will inch them that much closer to murdering a person for selling items without a permit.
Even if they make it through their whole career without becoming a murderer, they will justify the murders committed by their fellow Blue Line Gang members. They'll look the other way instead of defending the victims with deadly force from their gangmates. This is just as evil as committing the murders personally. You become what you defend and excuse.
If you care about someone, DON'T support their descent into the vile, nasty life of law enforcement. Encourage them to be a good person who contributes to society instead. No good can come of choosing to commit acts of law enforcement in exchange for stolen money.