So who is going to police federal laws? States cannot because if they did there would be 50 different interpretations/enforcement of every federal law. Talk about forum shopping.
Before the FBI, DoJ used investigators from the Secret Service, federal marshals, other law enforcement agencies, and private detectives to enforce federal laws. However, as the federal government grew, the need arose for a permanent law enforcement agency. We could get rid of the FBI but not without a true reckoning of the scope of federal power. You can't have a federal government this big and intrusive without the FBI or some agency that basically does the same thing. Can we have a serious discussion about that in our current society? I don't think so. We don't even know what the hell a boy or a girl is anymore, and Taylor Swift is worth over $1 billion. We're not going to have an intelligent discussion in this country about anything, much less an issue that requires some nuance and literacy.
Far more realistic than getting rid of the FBI would be a political overhaul of the agency. Almost the entire senior leadership needs to be not only fired but completely out of the law enforcement business, and in the DC field office, basically everybody above the janitor level should be fired. It's a political cesspool. However, we also need to come up with a different system for prosecuting federal officials. The idea that they get prosecuted by DC officers in front of DC federal courts and with DC juries is ridiculous. It's just too partisan of a venue to be taken seriously.