Cameron later recalled leaving the lunch with a completely different message for the producers: Schwarzenegger should not play Reese; he should play the machine. (BFI)
Schwarzenegger did not immediately celebrate the idea.
From his perspective, the change could look like a career mistake. Conan the Barbarian had established him as a leading man. Reese was the human hero of The Terminator, had extensive dialogue, had a relationship with Sarah Connor, and carried much of the story’s emotional explanation. The Terminator, by contrast, was the villain and barely spoke. Schwarzenegger has remembered protesting that the character had only about 27 lines. He worried that taking a nearly silent killer role after becoming a heroic lead might send his career backward. (Men's Health)
There was also a more basic problem. Schwarzenegger had read the script believing Reese was the opportunity. His fascination with the robot had been analytical, not an audition for it. He had effectively argued himself out of the role he wanted by explaining the other character too well.
Cameron kept pushing.