Screaming kids will always be present: it appears that some parents think of Disney as a place to let all manners go and to let a free for all take place.
As for screaming kids in the restaurants: I think that some of the more upscale/ and expensive restaurants should have an adults only section, where the constant screaming and running children are prohibited.
What I dislike the most are the drunk adults at the resorts: particularly the ASSports, where they hang over the guardrail on the upper floor and yell down to the people in the pool below. Worse is there attempt at drunken humour, which no sober person undertands or thinks is funny.
A few things that need to be added to the poll list:
1...back packs that are so large that they take up the place of one if not two people in lines and on buses. Once a back pack is so large that it takes a second person to help you get it on and off: it may be time to think that you are taking too much stuff with you.
2...rolling coolers: the paths are blocked now with strollers of all sizes and shapes. Rolling coolers and rolling suitcases have no place in the World: if you need that much material with you leave it in a locker, don't take it everywhere in the parks.
(What happened with the ban that used to be in place for rolling items???)
I have been going to both
Disneyland and Disneyworld since the mid 70's and I have seen a steady deterioration of the "family atmosphere".