Back when my son was being chaperoned a neighbor asked me why. I told him it was for their own protection. So he asks me "don't witnesses trust their own kids?". I stammered around some but had to agree. Witnesses don't trust their kids. Once when my son was driving his gf to the movies I followed him in our car. This way they could have some private time and discuss things without anyone over hearing. We got several phone calls from the "friends" about my son going out unchaperoned.
When elders called about it I gave them a ration of crap they won't soon forget. Funny thing is a few months later the PO's daughter was dating and doing exactly the same thing as my son was.