IMHO a threat to your physical safety demands you defend yourself by whatever effective means avail themselves to you; i.e. shoot.
Its not likely that I will be involved in a Spring Break situation. If I come upon a similar situation I wouldn’t be threatened unless I got involved.
All anybody had to do was yell at those aholes to stop and then take that girl away. I would have done it with no problem. Those kids are just opportunists who saw nobody would stop them from being who they are.
At the risk of being socially unacceptable I will say that when I was in college and at spring break at the S Fla beaches and Pananma City there were no Amish and there was a lot of drinking and carrying on but no gunfire and raping girls in beach chairs. Sorry but it is what it is.