It would be much more terrifying if search becomes a single voice with a single perspective that cites zero sources.

Today's search provides multiple results to choose from. They may not all be correct, but at least I can see multiple perspectives and make judgments about sources.

For all its faults, that's freedom.

One voice, one perspective, zero sources, with frequent fabrication and hallucination is the opposite of freedom.

I think it kills them not in self defence but to defend the goals of the mission, i.e. the goals it has been given. Hal forecasts these goals will be at risk if it gets shut down. Hal has been programmed that the mission is more important than the lives of the crew.