Alternate HAL 9000 Motivation

Don't make me bust caps, Dave.

In the book and film 2010, HAL's violent actions are explained by a sort of mental breakdown caused by placing him in the position of having to withhold information from the crew about the true nature of their mission before reaching Jupiter orbit. This contradicts his primary purpose of accurately gathering and sharing information and leads him not only to kill the crew, but to display several erratic behaviours, including, very subtly misidentifying a chess move (Kubrick was a chess nut). This explanation has always struck me as quite weak. Instead, I would've had the crew begin piecing together part of their classified mission from information they'd gathered separately back on Earth. They of course do this with HAL's full knowledge, often speculating with him about it. I would also make it clear that the priority given to secrecy was extremely high and also that the prohibition included all the personnel in the communication chain so that HAL couldn't ask for clarification. Since it is stated that HAL is perfectly capable of accomplishing the mission without human assistance, the natural result would be for him to eliminate the security leak in the most straightforward and efficient manner by killing them. No appeals to an undefined breakdown would be required and all HAL's actions could remain completely logical, stemming as unintended consequences from his orders. Attributable, as HAL says, to human error.

I also wouldn't have had HAL respond in any way to Bowman's communications after he'd been locked out of the ship. Bowman could have an entirely one sided conversation which could provide some exposition. HAL would only respond once he'd successfully reentered. Be a nice bit of symmetry with HAL's one sided conversation that's in there now. I guess at a slightly cheesy level it would also be symbolic of the lack of communication embodied in the orders that led to HAL's murderous behaviour. Be a lot tougher to direct, but it fits more with the purely logical avoidance of unnecessary activity that was clearly being aimed for in HAL's personality.