Their popularity is exasperating deficiencies. Magic Kingdom, for example, is seeing 10,000 more guests per day than it did 10 years ago. That's a lot of people. As I've said in the past, they aren't perfect and mistakes have been made but most of these issues can be boiled down to there simply being too many people wanting to visit the parks.
And I still maintain that Disney has demonstrated considerable constraint here in light of this. They could easily double the price of admission and all of this would go away.