With all due respect to Prof. Serrano, he's being naive, like a whole lot of his peers. He just got hit smack in the face with a case study in human nature, and he can't get his head around it.
Academic integrity exists on a Gaussian curve. For that matter, so can most of human group behavior. The people at the top of the curve scrupulously obey the rules, and the people at the bottom will violate them without hesitation for personal advantage. The overwhelming majority in the middle will follow the rules, but only so long as they perceive that the rules are applied fairly, and the people caught violating them are punished.
Cheating runs along the same scale. Most universities have honor codes, but an unenforced honor code is meaningless. A professor's job is to create an environment where students perceive that academic integrity is being enforced. That's what keeps most of them from cheating, not a signature on a honor code statement.
Prof. Serrano's first mistake was thinking that most of his students were inherently honest. They're not. Like all college students, they were only honest so long as they believed the rules were enforceable. AI changed all of that, and every student in the middle of the curve, even including most at the top, gave up. After all, why let your peers get better grades than you with almost no effort?
Serrano's second mistake was believing that the administration at Brown University was going to give failing grades to nearly a hundred students, or perhaps even suspend them from classes for a semester, and then have to face a lot of angry parents. Plus, how did Serrano expect to prove they cheated? A poor performance on a final exam doesn't necessarily mean they cheated on a midterm. I personally wouldn't turn the case over to an honor council based on such evidence.
Serrano learned his lesson the hard way. Take-home exams are dead and gone. The only evaluations you can trust are the ones that happen in a classroom, under supervision, without access to a smartphone or laptop. Serrano wanted to believe in an academic ideal that never truly existed. Artificial intelligence is forcing a whole lot of faculty in higher education to face a very uncomfortable truth about their jobs.