Shooting a 15 year-old girl’s dog right in front of her when she is an invited guest on your property, and there is no immediate threat to safety or property, is a dick move, IMO, even when it is perfectly legal. It is the kind of thing a total loser does to make himself feel like a big man.
Letting your killer dog run loose repeatedly to kill other people's pets, that is being a total jerk.
The man warned them of what he would do if it killed his animals. They paid their money and made their choice.