What would you do if your husband/the other parent did this?
That doesn't sound like the kind of man I would be married to. My husband is not that irrational (this situation doesn't create a particularly high risk of kidnapping) and if he disapproved of our child participating for another reason, he wouldn't stand by until she is already holding a sign and offering hugs before intervening. He also has this habit of using his words instead of just yanking our kids. So if my husband did do this, I would ask my daughter to stop arguing and help get daddy home, and then call a doctor because there is obviously some neurochemical imbalance or brain damage causing his weird behaviour.
How would she be kidnapped by a stranger in broad daylight on a busy street? Most kidnappings are done by someone the minor already knows, not a random stranger who wants a free hug.
He's right. By the way, your story is full of baloney. Nice imagination there. Any girl that is that dumb needs better supervision!