There’s no shortage of people ready to deploy "Thermian arguments" -- a logical fallacy arguing that any piece of media is beyond criticism as long as it makes logical sense within its own universe -- to explain the perfectly plausible, in-universe inclusion of the Iron Giant committing atrocities in Steven Spielberg's adaptation of Ready Player One. The novel, written by Ernest Cline, mentions the iconic, animated being in passing. The common argument for his movie appearance is that this isn't the real Iron Giant (though a curious number of Ready Player One devotees have explained to me why this also makes sense for in-universe real Iron Giant).
This line of thinking ignores that none of the logical explanations matter. This isn’t about the laws of the lush and textured universe of Ready Player One -- full of recognizable pop culture references (provided, of course, they took place before 2018) -- and whether they mesh with themselves. Instead, it's about how we -- in the real real world -- relate to media. Using the Iron Giant for evil sparked plenty of controversy; it was the rare children’s movie with a point of view and a message, a thoughtful, emotional tale about an autonomous weapon from space consciously choosing not to do the violence he was programmed to do. The Iron Giant is in Ready Player One not because this character, or even what the character represents, makes thematic or logical sense in the narrative, but because Warner Bros., the studio behind the adaptation, owns the rights to The Iron Giant. By its inclusion, Ready Player One takes a character from a pointed pacifist movie and scrubs it of all what made it unique and meaningful. The movie doesn't understand what it means to turn the Iron Giant into a weapon, and worse, neither do the characters. There's no actual nostalgia in this nostalgic epic.