We waited to go to WDW until our youngest was 4 so she would enjoy the place as well as being less likely to have a fit. Both kids did pretty good. The only real meltdown I remember was from our oldest at the Rainforest cafe. It was lunch so she may have been tired after spending 4-6 hours in AK.
She ordered hotdogs and when when she put ketchup on the dogs IT HAPPENED. The ketchup Got On The BUN!
The crying commenced. Cleaning up the bun was not enough. Talking. Reasoning. Nope, not working. The server was great! He brought out new hotdogs which stopped the crying. As a result got a big tip.

That is the only fit I remember from both kids.
We look at other parents dealing with a tantrum and just kinda cringe and smile.

Hoping we won't be in Tantrum Town anytime soon.

I don't remember seeing many fits at WDW. Issues with adults, we had a couple. But as other have said the only "problem" I have with a kids tantrum is if the parent is chewing the childs fanny so to speak. Kids have tantrums. How the parents deal with them is really the problem.
I was in the grocery store the other day. Usually my oldest is with me but I was alone. I wish she had been there to see what happened though. I would have like to see what she thought. There was a mother with an infant and a daughter that looked to be about 7. The seven year old was running around in the I Want This mode. Mom was calmly and robotically saying No.

I smiled at Mom since I have a closet full of the Been There Done That T-Shirts. We followed each other through the store and about half way the little girl, after being told "No." for the 101st time, said, "You are such a big MEANY!" I busted a gut on that one.
If I only had a penny for every time we heard that one we could live at WDW 365 days a year!
We are soon off to WDW again. The kids have learned the following WDW Mantra aka The Three Rules Of WDW.
1-There are No Fits at WDW.
2-There is No Crying at WDW.
3-Only Fun is allowed at WDW.
They do remember The Three Rules Of WDW.
Whether The Rules will rule is another story. And we may need to add Rule Number 4 after this weekend.
4-There is No Fighting at WDW. :lol
Later,
Dan