Don't convolute the issue with comparing to shoplifting. That has it's own complexities and generally as you say, people are instructed to report to the proper people, not act out alone. But that doesn't mean 'ignore it' - that means engage the people trained to handle it. But shoplifting is an entirely different subject. And even in those cases... they don't ignore the problem, they come up with deterrants.. like creating staff locations near the entrance... putting up monitors to re-enforce that you are on camera.. etc.
Focus on policies, not crimes.. and the acceptance of engaging with the customer is more accepted. For instance, walk into best buy and try to put something inappropriate on the stereo blaring loudly.. someone will engage you. Go into a store where the displays say "do not touch" and you start pulling them down and handling them.. someone will engage you. Walk into a McDolands with a KFC bucket, a big gulp cup, and fill up and start having your meal at a table.. someone will engage you.
Let's draw a simpler comparison for everyone. Someone sits down and lights up a cigar in the food court.. do you expect a CM will address the person, or do you suggest the right answer is 'do nothing' because they can't risk confronting an guest?
Even if Disney doesn't train all staff to handle the situation.. they could train them to engage the proper person instead of just IGNORING IT. If Old Navy, Target, and countless other retailers can afford to put a radio on all the staffers on the floor... Disney, who charges 2-3x normal rates, can't somehow figure out how to work out how to stop people breaking policies?
Maybe we should all just walk right past the cashiers in the food courts with our trays and see just how soon before Disney will somehow figure out how to 'allow' CMs to communicate with the guest breaking policy.