"The Great Wall" has all the makings of an epic action blockbuster.

It had a massive budget. It attracted a global audience (at least on paper). And it boasts one of the biggest Hollywood stars on Earth, Matt Damon — which, ironically, may have been part of its great downfall.

Photo by Robyn Beck/AFP/Getty Images.

Aside from the onslaught of poor reviews — "If ever a film was made with more money than sense, this is it," film critic Kenneth Turan wrote for the Los Angeles Times — "The Great Wall" is taking heat for its questionable casting decisions.

"The Great Wall," a film set in 11th century China, stars Matt Damon as the hero who saves the day. And that's more than a little cringeworthy.

There weren't a lot of Europeans in China during the Song dynasty (to put it lightly), so, even for a film whose premise hinges on conquering supernatural beasts, Damon's starring role seems a little too far-fetched for many audiences.

From a historical perspective, the absurdity of Damon's character reflects the film industry's terrible habit of whitewashing: casting white actors in roles that were created for people of color. (See: Emma Stone portraying Allison Ng in "Aloha," Jake Gyllenhaal as Dastan in the "Prince of Persia: The Sands of Time," and dozens and dozens of other films.)

Photo by Frazer Harrison/Getty Images.

If all races were seen frequently and fairly on screen, and if actors of color were cast more often in roles that aren't defined by the color of their skin, maybe whitewashing would be less of a problem. But that's not the case. Last year, researchers at at the University of Southern California's Annenberg School for Communication and Journalism found that women, minorities, and LGBTQ people were severely underrepresented among the over 21,000 characters and behind-the-scenes workers it analyzed in its study.

Unsurprisingly, the internet was not about to let Damon off the hook.

On Feb. 16, 2017, the day before the film's release, the hashtag #ThankYouMattDamon started trending, sarcastically thanking the star for his role in "The Great Wall" and all the other things he's contributed to Asian history and culture.

The trending phrase — created by comedian Jenny Yang — reached far and wide.

If it seems like the internet really has it out for Damon on this issue, it's because of his recent mishaps when it comes to speaking up about diversity.

In December 2016, Damon compared the casting criticisms of "The Great Wall" to fake news, then proceeded to defend the film by confusing whitewashing with race-bending (when white actors wear makeup to appear as a different race).

That came after a 2015 episode of HBO's "Project Greenlight," in which Damon caused a few jaws to drop for interrupting successful producer Effie Brown, a black woman, to explain to her how diversity works.

Except he got it wrong: "You [promote diversity] in the casting of the film, not in the casting of the show," he told her, trivializing the importance of having people of color working behind the camera as well as in front.

Eesh.

Although whitewashing may seem like a trivial issue — particularly in the uncertain era of President Trump — we shouldn't overlook its effect.

Not only does whitewashing sideline actors of color, limiting and typecasting the roles available to them, it prevents stories from marginalized groups and characters from being told authentically to a wider audience. And when people of color are represented on screen — like in recent films "Hidden Figures" and "Rogue One: A Star Wars Story," for instance — it makes a big difference to the people watching.

The diverse cast of 2016's "Hidden Figures." Photo by Alberto E. Rodriguez/Getty Images.

#ThankYouMattDamon laughs aside, actor Constance Wu captured the seriousness of whitewashing in "The Great Wall" — as well as creating narratives that solely celebrate white men as the heroes — in a viral post last summer.

"We have to stop perpetuating the racist myth that only a white man can save the world," Wu wrote. "It’s not about blaming individuals. Rather, it’s about pointing out the repeatedly implied racist notion that white people are superior to [people of color] and that [people of color] need salvation from our own color via white strength."

Let's hope Damon's somewhere taking notes right now.