That was a huge issue with me, after my ex slandered me 20 ways to next Tuesday, during our divorce.
I had a poster hanging on the hall, said: "A lie unchallanged becomes the truth"
I'm glad you brought this up, (not that I'm glad this happened to you of course), because I wanted to mention the way parenthood has been undermined as an example of "progress" I'd like to see reversed!
During my battles to try to stay in contact with my one child, (then aged twelve), an appearance at a court sponsored meeting occurred, where my daughter was sat opposite to me on one of four chairs, arranged in a square or diamond, (if you see what I mean).
Two court officers sat on the other two chairs, (who were trained no doubt to deal with children where their parents are in conflict over them).
My daughter was then invited to say what was wrong with me, the contact I had with her, and even her feelings or lack of feelings towards me.
In my view the courts thus gave my child an opportunity to pillory her father, and she was no doubt told "this was her right",(or at least her right to comment, which can amount to the same thing).
I declined the opportunity to say to my daughter, "even though you said you hated me, and I was horrible often enough during our weekly/fortnightly contact visits, you then went on to say, "Keep coming daddy didn't you", (because I don't believe it right to be expected to defend yourself in this way in front of strangers, even if I imagined they'd listen).
The male court welfare officer, a wisend looking chap, was sufficiently convinced he'd understood everything about our relationship within five minutes declared, "I can see there's no positive relationship between you"", and the woman court welfare officer agreed with him, (who just happened to be pregnant so couldn't be cross examined when her report got back to court because of maternity leave).
I've bored you all with this on a thread having nothing to do with fathers/parental rights etc., for this reason, "The undermining of the institution of marriage, (for good or ill for the men and women involved), has consequences well beyond those two people involved, obviously especially where children are involved, but beyond even that I believe".
A child being shown those in authority may think its okay to denigrate one of your parents, and in front of them, is not benign. Even the setting up of the chairs was a significant factor I believe, not having my child on the chair beside me, as though those two officers had to be between us or come between us, and my daughter had the same status as myself which she should have in my view, or else I become at least equal to a child, (and I'd argue I'm being treated as a child by those court officers).
Beyond that it speaks to truthfulness, and whether you're believed by those in authority when you speak the truth, (as I did when I said I beloved my child enjoyed the contact, and much as she told the court officers she didn't see me as her father she couldn't stop herself calling me "dad"!).
Lying helps you win is one of the messages to pick up on here, "in the modern world", and "government appointed officials can reach right into our private lives,", (undermining and destroying them in my view as I've said!).