It's like in 2001: A SPACE ODYSSEY when things go wrong with HAL. I accept that plot twist, but it's not really what the movie is about. It's about getting to Jupiter and I would have been just as happy if they got there without a hitch. Surely the Monolith didn't figure on them having a computer fiasco and I have a hard time believing that Bowman was actually able to get there after that disaster happened.
Actually, since the movie is about phases in the evolution of sentience, what happens with HAL is integral to the overall theme.
There came a time when the Old Gods died! The Brave died with the Cunning! The Noble perished locked in battle with unleashed Evil! It was the last day for them! An ancient era was passing in fiery holocaust!