The fact that this system can be exploited by neo Nazis should tell you that it can be exploited by anyone. Including the cops who will be investigating these complaints.

Non-public and anonymous are not the same thing. I don't know about your jurisdiction but when you file a criminal complaint police do take down your name and address, if you're worried about retaliation or such there's ways to have all public records under a pseudonym and e.g. your lawyer's address, but the state will still know who you actually are.

You can also give an anonymous tip to the police -- but those don't ever reach the level of complaint. Police and prosecutors can toss such a statement without much fanfare, even if they don't they can't follow-up with questions, you're way less credible as a witness, especially since you can't be nailed for false accusation, at least not without investigators hunting you down. You can't file an accessory suit (that is, be a co-prosecutor) because courts definitely don't deal with anonymous people, if they anonymise the public record then because they think it's the right thing to do to serve justice, not because you don't want to show your face to at least the judge(s).