The term scared straight worked its way into the American vernacular after a landmark 1978 documentary by the same name. This documentary featured hardened criminals in prison talking with (and often shouting at) teens who were headed down the wrong tracks. The idea was, if some of these straying teens could get a glimpse at what might await them if they didn't get their act together, perhaps they could be "scared straight", that is, maybe this shocking dose of reality could prompt them into making better early-life decisions.
In the article, the author isn't talking about youth headed toward a life of crime, but how customers regard and treat the wait staff at a fine dining establishment. Those who have never "seen the inside" (a phrase that would refer to a serving time in a penitentiary in the original documentary, but, in the Salon piece, the phrase would refer to working at a restaurant) are more apt to treat wait staff with rudeness and condescension. So, the author is saying that everyone should have to wait tables at some time, as it would "scare them straight" – that is, it would dissuade them from lingering in the dining room long past closing time, or stealing a restaurant's centerpiece for a souvenir. I think the "scared straight" reference sets up this sentence in the following paragraph:
A required year on the front lines would not just be a refresher in simple good manners, but the reminder of the underlying purpose of those manners.
In other words, if you learn what it's like to have those things happen to you while you are "doing time" on the restaurant staff, your restaurant behavior will likely be straightened out for the rest of your life.