LOS ANGELES  - When Kenneth Branagh cast Idris Elba as Heimdall in the upcoming summer movie "Thor," some fanboys furiously insisted it was wrong for a black man to play a Nordic god often described as "the whitest of the gods."

Fumed one fan in an online forum: "This PC crap has gone too far! Norse deities are not of an African ethnicity! ... It's the principle of the matter. It's about respecting the integrity of the source material, both comics and Norse mythologies."

Wrote another on TheEscapist.com: "At the risk of sounding like a bigot, I think this is nuts! Asgard is home to the Norse Gods!!! Not too many un-fair complexion types roaming the frigid waste lands up there. I wouldn't expect to see many Brad Pitt types walking around in the (first mainstream black superhero) Black Panther's Wakanda Palace!"

Replied another: "It's their right to be honest, I still refuse to watch the whitewashed Prince of Persia. Not that I'm racist, I... hate racists, it's just Hollywood (messing) with the natural order of things. Wouldn't be surprised if this is a planned publicity stunt."

But the London-born actor (who starred as Stringer Bell in HBO's "The Wire"; his 2009 film, Obsessed, grossed $68 million domestically) has no patience for the debate.

"It's so ridiculous," he said during a recent appearance at Rutgers University in Newark, N.J.

"We have a man (Thor) who has a flying hammer and wears horns on his head. And yet me being an actor of African descent playing a Norse god is unbelievable?" he went on. "I mean, Cleopatra was played by Elizabeth Taylor, and Gandhi was played by Ben Kingsley." (Kingsley's father was of Indian descent.)

Beyond that artistic defense, though, there is an even more basic reason black actors welcome colorblind casting: There is a ceiling on the amount of business black-themed movies can achieve, so the opportunities for black actors and actresses remain limited unless they can also claim parts in mainstream entertainment.

In the past decade, black actors have been losing ground. In the early 2000s, blacks played 15 percent of roles in film and TV. Today, it has fallen to 13 percent, according to Screen Actors Guild stats.

Will Smith is one of the few African American actors who has transcended racial barriers, with his movies grossing $2.52 billion worldwide -- not far behind the $2.87 billion collected by Tom Cruise films.