Clarke's Law is sophistic poppycock to justify the author doing whatever they want without having to explain it. It's a fancy sounding way to say their doing an asspull.
That's not true at all. You're forgetting that Clarke was a science writer as well as a science fiction writer. Clarke coined the phrase in the revised edition of an essay called "The Hazards of Prophecy" in his nonfiction book Profiles of the Future. The theme of the essay was that we are limited in our ability to predict the future because of the limitations in our knowledge. Physics or technology that were dismissed as impossible, magical dreams by one generations have often been achieved by a later generation, because they figured something out that never occurred to people before them.
As to the rest, HAL is a machine, that's the point. He is limited. Responsibility to think beyond his programing? Responsibility is irrelevant. He's a machine and incapable of those questions. That's why he's not evolving beyond his state unlike Dave or the apes earlier.
The whole point of HAL is that he's a Heuristically programmed ALgorithmic computer, which means a neural network that learns from experience (heuristics) and can therefore grow and innovate in the same way a human mind can. The fact that he's more than "just a machine," that he is capable of growth and change, is the very thing that he's named for. HAL was a breakthrough in artificial intelligence, a computer that thought and learned like a human. That's why he was taught by Dr. Chandra to sing "Daisy Bell." He wasn't programmed like a conventional computer, he had to learn like a child. That's what "heuristic programming" means -- learning by doing, forming behavior and knowledge through trial and error and reinforcement. If he were just a mindless mechanism, he wouldn't have been able to act as he did in the film, spying on the crew, hiding things from them, defying their orders. He was capable of independent thought, will, and choice. That's intrinsic in everything about the character, including his very name. HAL was more a person than a tool.
No kidding, the sentinel was an earlier story. Wow, so what. The movie is not the sentinel nor is it beholding to it anymore than Forbidden Planet is beholding to the Tempest or even to the book. Viewers certainly are not beholden to the book for their interpretations. That's the beauty of thinking beyond the programming.
"Beholden?" It's the other way around. If you only consider the movie and ignore the book, you're deliberately settling for incomplete information. Yes, the stories are different, but being familiar with both versions can deepen your insight into both versions.
It's one thing to say you prefer the deliberate ambiguity of the movie. But if you assert what you claim to be a single, unambiguous reading of the film, yet simultaneously reject the insights offered by the version that actually gave a clear reading of its events, that's contradictory. You can say the film allows for more interpretations than just the book's, but it makes no sense to say the book's is simply wrong.
And the Forbidden Planet analogy doesn't work at all. That film was only very loosely inspired by a centuries-old play. The book and film of 2001 were developed simultaneously and symbiotically. Both are the work of Clarke and Kubrick in collaboration, differing only in the ratio of their contributions. They're telling essentially the same story about the same characters; aside from tweaks like whether the Monolith was at Saturn or Jupiter, they differ mainly in the style of how they present the story. They depict the same events and processes, but Clarke explains the background while Kubrick does not.