Tyler "Madea" Perry, playing ex-cop and FBI agent Alex Cross? Height- challenged Tom Cruise as 6-foot-5, 220-pound former Army military policeman Jack Reacher? As far as some fans of the books featuring these characters are concerned, the casting gods have gone absolutely bonkers, putting two actors into roles they are totally unsuited for.

"How does anyone think that Tyler Perry looks right for this role?" says one posting on Screenrant.com, after seeing the trailer for "Alex Cross," which opens Oct. 19. "Madea has better acting from Perry than this movie."

Over at jackreacherfan.com, where reaction to the Cruise casting in "Jack Reacher," opening Dec. 21, has been almost 100 percent negative, one posting noted, "I cannot grasp the content of the conversation that took place where anyone could possibly have agreed that this was a good choice. Have they EVER read one of the books?"

And so it goes. Take an iconic book character, look for the right actor to play him in a film, and wait for fan blowback.

"People always get up in arms when it's a character in a book they love," says Alexa Fogel, a New York casting director who has worked on "The Wire" and many other TV series and films. "When it comes to serial literature, the audiences are really protective of that environment," she adds. "They probably have owned the material for the years they have read it. But in the end, I don't think it affects who goes to the movies."

When you're dealing with studios, high-profile book projects and big budgets, fan expectations and desires don't affect casting decisions. It's either "What young actor do we think is right for the part?" -- think Jennifer Lawrence in "The Hunger Games" or Robert Pattinson and Kristen Stewart in the "Twilight" films -- or "Who can put butts in the seats?"

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In the case of Jack Reacher, for example, Paramount bought the rights to "One Shot," the book on which the film is based, and set up Cruise's company to produce. One of the biggest names in the business wanted to play Reacher, a 40-something former military cop who roams the country with literally nothing more than the clothes on his back and a toothbrush, never looking for trouble but always finding it. Given that the series -- the 17th book, "A Wanted Man," was released last month -- has more than 60 million copies in print in 96 countries and nearly 60 languages, you can bet thoughts of a worldwide cinematic smash were dancing in Cruise's head. "You can't finance a huge movie today without someone who plays into the international box office," says L.A.-based casting director Marcia Ross. "An actor like Tom Cruise brings some other needed things. Economic considerations play a huge part in the decision-making process."

And it doesn't hurt that Lee Child, author of the Reacher series, is totally fine with the casting. "Cruise is a character actor," he told Time magazine. "He really gets into the role. He can understand the role. He can project the vibe. But the only real answer is to go see the movie. I guarantee you will come out of it and you will think, 'What was I worried about?' "

"Jack Reacher" is the first film of a potential franchise. "Alex Cross" is the third to feature the D.C.-based character, once a cop and FBI agent, now working as a private detective and psychologist, but who continues to consult with his former employers on a variety of cases. Cross has been the protagonist of 19 books, which have sold more than 80 million copies in 41 languages and 36 countries. The first two films, "Kiss the Girls" (1997) and "Along Came a Spider" (2001), which starred Morgan Freeman, grossed a total of $210 million in adjusted box-office income, which means, as far as the studios were concerned, this cow had a lot more milk to give.

But, says James Patterson, author of the series, "studios were not willing to step up and make the movie with Morgan; they thought he was too old . That went back a ways. I thought of Tyler early on; I've seen all his movies, and I did feel he was a possibility. He is a lot closer to the character in the book than Morgan is, in terms of his age and his size. I met with Tyler, found him very smart, very focused. And, he said, 'I wouldn't attempt this if I didn't know I could pull this off.' And I felt he could do it."

So the bottom line is that all this blogosphere controversy is just so much yadda yadda. It certainly doesn't affect casting decisions. And going on the premise that if people are writing about it, they must be interested in it, the feeling is that the controversy over the Cross and Reacher castings can't possibly hurt their films' box-office potential.

The controversy "will have a positive effect," says Patterson, "because people are interested in this [film] and curious about it."

Adds Ross: "I think it's great for these movies that so many people are writing about them. At the end, if people like the movie, nobody remembers ."