Agreed, Jeffrey Epstein was a FBI informant according to court documents from his 2008 arrest. For which they would not prosecute him or his clients.

However the FBI is the USA's main defense against infiltration by Chinese, Russian and Israeli spies. Without a federal law enforcement agency we have no defense against this whatsoever. So if you "defund the FBI" what are you going to replace it with? You cannot just allow foreign nations unfettered access to the United States and we need a federal law enforcement agency that can identify foreign threats that have come inside our borders. So in my opinion defunding the FBI without a replacement agency in place would create a National Security crisis.