To place the blame for the seemingly increased instances of families who dine with children in tantrum mode on the dining plan is rather simplistic. Many families find it a great way to cut the overall cost of an already expensive vacation, my own family included.
We learn table (and other) manners at home first. It makes no difference where we dine, manners are manners, even at McDonalds. Children who learn what is and is not acceptable at the dining table are equipped to dine anywhere, including the U.S. Ambassador's residence at the embassy in Madrid. They have no dining plan, BTW
However, while children can learn anything, they are still children, and lack the emotional maturity to overcome fatigue and over-stimulation. Parents need to respect their limitations and plan their schedules accordingly. It's as simple as that. While I don't appreciate a screaming child next to me, I have compassion for the young mother who is struggling to calm her toddler when she herself probably feels like crap and may be trying to formulate a plan to get back to their resort at the other end of WDW while knowing her other kids STILL have to be fed and that staying put is the fastet way to get food in their stomachs. Yes, they might have chosen a restaurant better suited to their family's needs.... but for whatever reason they didn't. It's not my business to know... and it's not an excuse to call these people childish names... hopefully the incident is a lesson for them as parents.
Perhaps an even deeper cause is that families don't use the dinner table to connect socially and interact with one another. We use our table time to discuss what the best parts of our day were, what looks good on the menu (if we're dining out) or discuss family news. We enjoy spending time with one another... and while food is important, it's only secondary to the sense of togetherness. Spending our meals this way allows us to focus on one another and enjoy eachother rather than get our attention hijacked by unusual diners around us, unless they are a catalyst that allows me to spew sage advice to my kids
Be happy... be appreciative... be kind. Everything you swallow, including your food, will taste better...