I found it quite disconcerting when I first read about it, but thought the alarm bells I was hearing in my head may have had something to do with my own cynical, jaundiced view of life. It was interesting for me to read the comments from both male and female BetterMostians, verifying my initial view.
In their defense, the fathers who belong to the Purity Balls movement, probably also belong to such organisations as Father & Son. As I have no knowledge of the inner workings/philosophy of F&S, however, I regret my inability to comment on whether or not they are concerned with preserving the boys' "purity," which appears to be the primary underlying philosophical premise of PB.
One can't help but wonder if a lot of what's behind this is the parents (for I have no doubt that this also has the support of the mothers) looking out for their own interests, comprising of generous dollops of good ol' fashioned "What would the neighbours think?" if, heaven forbid, the daughter should ever "fall" pregnant.