I'm hoping that I have some karmic luck, because long before I had children I always thought children in restaurants made the place more fun and provided a floor show of sorts to watch. Perhaps because growing up my family ate out, on average, 6 nights a week (my mother had many incredible talents, but cooking was not one of them!), kids in restaurants have never bothered me.
I agree with all the posters who said that most of the issues seem to stem from parents who are either: A) too tired to enforce the rules, B) too indulgent to require basic manners and courtesy from their children, C) too focused on the trip to know when it's time to call it quits (for the day or even for 15 minutes while the child winds down), or D) simply too clueless to realize that their child's behavior is not "cute" to anybody else.
Our children, now 5 & 2, have eaten in some of the best restaurants in the world, and generally they are very well behaved. My DD5 knows, however, that she gets one warning and that consequences (generally just flat out leaving) will follow. Our son, who is 2, has some special cognitive needs and is also a two year old in spirit and mood, so reasoning with him is much more of a challenge. We have to read his mood, anticipate how the evening will flow, plan ahead, and even, on occasion, cancel our plans rather than risk a fiasco. But that's life as a parent, and a night in with a pizza or takeout can be as much fun, albeit in a different way, as a night out at a restaurant.
In summary, some poorly behaved kids and loutish adults will be everywhere at WDW. Since all of us have to deal with the behavior of those around us, to all guests I simply ask: don't be a jerk!