Everyone is biased in some way or another, and to think otherwise is naive and foolish. You can't get rid of bias anymore than you can get rid of emotion or opinion. Best way to deal with bias is recognize your bias so you can adjust your actions to compensate for it. Would you rather him lie and say he isn't? None of us have ever claimed to be unbiased, we do try our best to not let it interfere with our duties.
Absolutely true.
As for the OP, Nefario isn't responsible for the actions of others. If Usagi/Diablo is a scammer, you don't blame the middleman unless you can prove he knowingly aided and abetted it. Innocent until proven guilty and all that.
Once Nefario used his position of authority to act in a certain way, all the people harmed by his failure to act in the same way in the same circumstances had a legitimate claim against him. This isn't me making shit up, this is 500 years of established equitable practice at common law and possibly more than 500 years in the civil system. You might not know about this, even if it's basic and well known in the legal profession; it's obscure from a public PoV, and I guess nobody told you to go to law school first if you want to be a mod on some forum. However, you must know socially someone who actually is a solicitor/barrister/etc. Ask them.