In your post, the definition of "E-Ticket" seems to vary from "thrill ride" (as in, why expect a "thrill ride" in Fantasyland?) to "income generator" such as 7 Dwarfs Mine Train - and "Its a Small World"
was an E-ticket, to prove your point as it is no thrill ride by modern definition.
http://www.yesterland.com/abcde.html
So to answer the question of why not to have an E-Ticket type
thrill ride in Fantasyland? My answer would be "because each time a thrill ride has been added at the Magic Kingdom, it improved the park experience for many people. Space Mountain was added to Tomorrowland. Big Thunder and later Splash Mountain were added to Frontierland. At Disneyland, Indiana Jones was added to Adventureland. None of those were opening day attractions and all are without question some of the most popular attractions at either park.
Now, to tie this into the SPIRIT of the thread and not be argument simply for argument's sake, I would say most everyone who visits the Magic Kingdom spends some time in Fantasyland and not just the crowd content to go in circles. If the new leadership of the Imagineering department might be tasked with considering new Fantasyland attractions to be added years from now, I would be hopeful and optimistic that the voice of Walt Disney World fans who want more than to go in circles might be heard and a thematically appropriate attraction might be considered.
Just because some might view the Fantasyland area of the Magic Kingdom as having been the equivalent of the petting zoo to the entire zoo for the past almost-50 years doesn't mean it has to be that way forever.