"It just made so much sense, and I couldn't imagine it being anyone else," Watts said.
Why not? Keaton, of course, would bring his own meta-history to the role, having gone from playing a brooding Batman to an over-the-hill Birdman and now, another winged, super-powered egomaniac.
The filmmakers eventually landed Keaton, and his performance in "Spider-Man: Homecoming" has been hailed as the best comic book movie villain in ages. The Times' Kenneth Turan praised Keaton's Adrian Toomes, a.k.a. the Vulture, as "one of the strongest, most sympathetic villains of the entire series."
Toomes makes an ideal foil for Tom Holland's teenage Spidey because he's just like Peter Parker, a friendly neighborhood guy who stumbled on great power and is trying to use it to correct the wrongs in the world. (Warning: Spoilers ahead.)
The big difference? Toomes thinks he's the one who's been wronged. A blue-collar salvage company owner who saw his livelihood usurped after the events of 2012's "The Avengers" by billionaire superhero Tony Stark's new cleanup contract with the government, he takes a moral sidestep to stick it to the system and provide for his family.
In the process, he becomes a small-time weapons dealer, selling scavenged Chitauri technology on the black market. Before and after we see him wreak havoc across Manhattan as the mech-winged Vulture, we understand his motivations come from his desire to protect his own.
" 'Spider-Man' is the idea that you're going to take a regular guy and turn him into a superhero," Watts explained. "I loved the idea of taking a regular guy and turning him into a supervillain — what would that look like?"
The challenge for the makers of "Spider-Man: Homecoming" was to find a fresh take on the Avengers universe and canonical events established over the course of 15 movies since 2008's "Iron Man." That brought Watts and the film's five other credited writers — Christopher Ford, Jonathan Goldstein, John Francis Daley, Chris McKenna and Erik Sommers — to the ground-level perspective of the everyman and woman who've been watching Iron Man, Thor, Hulk, Black Widow & Co. save the world from afar, the people left behind to sift through the rubble when the Avengers go for post-battle shawarma.
"Very often in a movie, you're telling the story of the elite," Watts said. "In Marvel movies, you get to see the story of a playboy billionaire inventor, you get to see the story of a Norse god, you get to see the story of an American icon. Every time I'd see one of these movies, I'd wonder: 'What is it like for a regular person? What does just a regular human being who lives in New York City know about this event, or think about this event? Where is public opinion?' "
Viewing the same events of the MCU through different eyes opened the world of "Spider-Man: Homecoming" to a fresh angle: In its opening moments, we see Peter, jazzed to be a part of the Avengers, soaking up every star-struck moment as he joins the airport battle from "Captain America: Civil War."
But on the flip side of Peter's wide-eyed fanboy wonder, there's Toomes. He is, as Rolling Stone posited, a "sympathetic Trump-era supervillain" who vaguely resembles the cliché of the Disgruntled American Trump Voter: alienated, economically anxious, white, middle-aged and male.
Watts is careful to leave politics out of his "Spider-Man" chatter. He describes how changing the optics on the events of films from "Iron Man" to "Civil War" opened up the Marvel franchise to smaller-scale villains than the Doctor Octopuses or Green Goblins of Spidey lore.
"When you start applying that kind of logic to the universe, it opens it up in a really funny way where you're getting this ground-level perspective. What does the world think of Tony Stark? What does a regular guy who might get put out of a job think about him?"
As a result, we get a villain who isn't just at odds with his daughter's prom date, but one who menacingly reveals his teeth when he realizes said kid is the masked vigilante who's been trying to ruin his booming black-market business.
He also poses a sympathetic philosophical challenge to what Stark and his cottage industry of superhero national security agents represent, building on thematic seeds planted in the first film.
Ultimately there's more Toomes than Vulture in Keaton's take on the supervillain. You might say there's a ... multiplicity of Keatons on display in the actor's performance.
"I couldn't stop thinking about him as this guy who's on a cleanup crew, who has his own small salvage business, getting screwed over," Watts said. "And you start to think of the other kind of Michael Keaton performance and realize, now I get to do everything — I get to have cool blue-collar Michael Keaton, I get to have awesome supervillain Michael Keaton and I get to have cheesy dad Michael Keaton."
Now that audiences have had a chance to see "Homecoming," Watts finally can freely discuss the secret twists of Toomes' double life.
"I can't imagine what M. Night Shyamalan felt like promoting 'The Sixth Sense,'" laughed Watts. "How do you do that if the whole time you're worried about saying, 'So, he's a ghost …' "