Well...it's a functional strategy, but you're basing it on a false analogy. Lions gotta eat. The choice for a lion is, eat this gazelle or eat that gazelle, or starve. Teenagers don't gotta punch someone unconscious. Their choices in life, no matter how bleak, simply aren't limited to which person they punch.
No but you do need to change the cost/benefit ratio somehow. that is what is key to this really. Or they simply get bored and move on.
Agree with Jon's assessment. This concerns me more than robbery as they simply don't want something. With Robbery violence is a secondary affect of the crime, a means to the end. with this it is the endstate, so you have a very difficult time affecting that endstate with "soft power". That is, reducing your risk by not wearing valuables, walking with a friend etc.
In this crime, these things simply may not matter. Again, what I think increases the cost benefit ratio is that bystanders will not accept it and will act in some way. Increase the risk of punishment, then this behavior simply stops as it becomes too costly to engage in it.