Therein lies the trouble!!
We here in Canada are so used to the petty crimes, it's a normal every-day occurrence. Nobody cares... signs of the times!!
But then, when these sunglass-cases move up the crime ladder and reach beatings, rape, drug smuggling... well, then ...o.k.... perhaps we should do something about it.
Nib it in the bud, I say! Don't belittle or put up with such behavior... not at all! If the kid didn't get it straight from home, then society has to teach what's right and wrong to him/her.
Are you contending that stealing sunglasses leads to more heinous crimes, like it's a gateway crime? That's one hell of a slippery slope if that is indeed your contention.
There is a huge difference between belittling something and using context. Teenagers aren't exactly known for having the best judgment, but most will learn lessons from such lapses. I suppose we could punish them harshly, and send them to the correction system, aka as crime school...