Some kids are prone to tantrums, some are not.
Some parents yell a lot, some do not.
Why would anyone expect things to be any different at WDW?
Further, as several have said, you are witnessing a brief moment in the lives of those people. Would you want somebody to judge you by what could be your worst moment of the day, or even week?
For every one child you see crying, or "obviously over-stimulated", dozens, or even hundreds walk by without even capturing your attention because they are not crying or over-stimulated.
In 5 minutes, that same crying child may be perfectly fine, and one of the "angels" you saw might be crying somewhere else.
Such is life, and we see it on a smaller scale at our local department stores every day.
Perhaps if we all kept things in that context, we wouldn't be disturbed so much by it that we are lecturing about it months after we last went to WDW.
I'm sure I saw a crying child or two on our last trip, or a parent who didn't seem to be handling things the way I thought they should. But you could offer me a billion bucks and I still couldn't tell you about a single specific incident.
The vast majority of people are trying to do their best, and despite what some say, the vast majority are having a great time.
As far as our particular style, we have roughly the same expectations and rules for our son as we do at home, or when at the mall. There's no way in heck that he's having an ice cream sundae for lunch, and since the answer at home is no, he's not surprised when the answer at WDW is no.
He doesn't get a toy at every store we walk into at home, and he doesn't get one at every store in WDW.
If you walk by while I am giving him a stern "no" that he's not happy about, well, you can rest assured that we are indeed having a wonderful time, but are just having one of those necessary moments that are a part of him growing up and me trying to be the best parent I can be.
Come back 5 minutes later and you'll see a more representative picture.