"Unfortunately, a lot of people in Hollywood believe that in order to have a better chance of making a profit on their films, they have to get a white actor."
McGowan has been cast to play Ben Kanahele, the man credited with saving lives on Niihau when a Japanese pilot crash-landed on the island after the attack on Pearl Harbor.
After being helped by Niihau's residents, the pilot subsequently colluded with inhabitants of Japanese ancestry to take several people hostage and terrorize the island over the course of several days.
Kanahele was eventually able to kill him in a struggle, but was also shot three times in the process. He later received the Medal of Merit and a Purple Heart.
Historians say the "Niihau Incident" increased fears about Japanese nationals and Japanese-Americans in the United States, and helped lead to the mass internment of tens of thousands of Japnaese-American men, women and children.
"Niihau" writer and director Gabriel Robertson said he wanted to make a film about the Niihau battle because of its "huge historical significance."
He told Deadline that the story "plays out like a Shakespearean tragedy. ... I see circumstance as the true antagonist of this story. These characters, once placed in this situation, were driven by their initial instincts: to help a stranger in need. Indeed, it wasn't until circumstance forced their hands that the characters desperately turned to violence."
McGowan has previously appeared in "Black Sails," "Shameless" and "The 100."
On Twitter Tuesday, he shared a link about the casting news and wrote, "Excited about this project!"
That prompted rebuke from some, and praise from others.
"You shouldn't be excited, you should be embarrassed to even think about whitewashing history," wrote one Twitter user.
