By bitcoin fraud do you mean frauds that are 'settled' in bitcoin or counterfeiting? The protocol stops counterfeiting, the miners stop individuals from failin

By bitcoin fraud do you mean frauds that are 'settled' in bitcoin or counterfeiting? The protocol stops counterfeiting, the miners stop individuals from failing to fulfill a payment (i.e. stops double spends) and theft is governed by whatever jurisdiction the crime happens in. The US government does not prosecute thefts of USD in other countries.