NTSB investigations are not criminal proceedings.

Yes. If justice means a criminal going to jail, defense attorneys do stand up and fight tooth and claw to prevent that happening. That is thier job. It is the job of the prosecution, the government, to overcome and enforce justice.

I don’t think that’s what justice means. Justice means that only people who a jury believes are guilty of a crime beyond a reasonable doubt go to jail. Defense attorneys serve that definition of justice. One could argue that prosecutors stand in the way of justice because their job is to put someone in jail regardless of whether they are truly guilty. In reality, the adversarial system is justice.