Say an abusive relative harasses and sexually abuses you, but you have no video evidence or witnesses. When you file a civil case against them for those things, they lie to the court and say you are delusional and are experiencing hallucinations. They use your low-income and poor resume as evidence to support their false claims about you. The court buys into their bullshit. Now what?
If you say they are lying, they try to instituionalize you by using your claim that they are lying as evidence of psychosis against you -- even if you are telling the truth. If a court orders a forced evaluation, and you tell the doctor the truth -- which is that they are lying -- and the doctor sees this as evidence that you are psychotic and gives you a diagnosis, can absolutely anything be done in this scenario? Or do the abusers get away unpunished and get you forced into involuntary psychiatric treatment? Moreover, they can use this as a threat to dissuade an appeal or any further litigation. It seems highly unethical and very illegal, but impossible to prove. And so basically, anyone can violate the family code freely as long as they can pull off that argument. The implications of this are horrific, pure lawlessness.
If they can easily do that, just by lying, that seems to make family law totally useless and dangerous.