I am prepared to accept, even argue, that many or most FBI agents are fundamentally decent people who got into their jobs because they want to make a positive contribution to society.
That does not mean the FBI in this case was acting decently, nor in many other situations. Power structures attract people who exploit systems for personal gain, and absolute power can corrupt. I don’t even know how I would function in such an environment, I am as vulnerable as the next to groupthink, tribalism and jumping to conclusions.
All that said, the man was innocent and got treated like a monster. Treated monstrously, despite a total lack of evidence. This is a problem. Any power structure in which it is possible to destroy (or even end) the lives of others must have a strong, third party oversight system of accountability. The FBI might be a good agency, or not. It is not run by gods and is subject to human fallibility. Since the rest of you are then subject to that same fallibility, you want to be very sure that the FBI is tightly overseen.
We have similar problems here in Canada. It is a delicate balance. On the one hand we want the police and security agencies to protect us, capture criminals and where possible prevent crime. On the other hand we don’t want to be abused, mistreated or wrongfully persecuted. Our police forces are badly out of balance right now and in desperate need of oversight and accountability.