What risks are associated with staying chaste?
I think that the parents did wrong, but I also think that willful ignorance of your child's habits is just as wrong. Simply sending them to an abstinance-only sex ed and then blithely assuming that they're not going to have sex is naive at best.
None that I am aware of but that isn't the point.
When I was a young man, I was sure it was going to kill me.