A discussion about "dream casting" for the upcoming Marvel Cinematic Universe version of the Fantastic Four turned into a debate about diversity (or a lack thereof) in the fan casting of many of the people participating in the exercise online. Asking fans who they would like to see cast in an upcoming superhero movie has been a fun thing for fans to do for as long as there have been movie versions of superhero characters, but this debate took on a whole other direction. RELATED: Fantastic Four: Valeria Richards Is Named After Doom's Long Lost LoveIt all started when Twitter user Luke posted his dream casting for the Fantastic Four on Tuesday.

His picks were Brandon Routh as Reed Richards, Dianna Agron as Sue Storm, Lucas Till as Johnny Storm and Drew Powell as Ben Grimm.

This led to many other fans coming up with their own dream castings over Tuesday and Wednesday. Some serious, like Trashyy05...

Who picked Brandon Routh as Mister Fantastic, Gillian Jacobs as Invisible Woman, Avan Jogia as Human Torch and Dominic Purcell as The Thing.

And some joking, like Gleb Melnikov's idea of casting the gang from It's Always Sunny in Philadelphia as the Fantastic Four...

or Tanner Slavin's idea of casting the main characters of The Good Place as the Fantastic Four...

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A common choice on the fan castings was married actors John Krasinski and Emily Blunt as Reed and Sue Richards...

However, other fans online took issue with the fact that nearly all of the fan castings involved all-white casts for the Fantastic Four. The most recent Fantastic Four film famously cast African-American actor Michael B. Jordan as the Human Torch, and so many other fan castings picked diverse cast choices.

Naturally, though, for every action there is a reaction and for every online reaction, there is a backlash, so other fans started to defend the idea of casting an all-White Fantastic Four cast.

The great comic book writer Fabian Nicieza, for instance, suggested that the Fantastic Four is "white bread," so he went with an all-White cast...

Either way, we will all find out soon who actually gets cast in the upcoming Jon Watts-directed film (there are already rumors that Jennifer Lawrence might be cast in the film).

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Source: Twitter