: I don't think a lot of people questioned it because the characters in the
: book all treat it as something bad, the only real debate is whether it was
: necessary. Haverson believes it is because the Engineers can't help
: themselves—they'd ultimately be aiding their enemy in a wartime situation.
: And everyone moves on because they have bigger fish to fry.

I get why he did it, but did he have to do it at a point in time where they weren't in immediate danger of getting captured?
The engineer had learned a valuable skill (repair of Mjolnir armor/shielding), and it was fairly secure with them. They could have used him to improve/repair the tech of the other Spartans (as well as their AAs), and resort to killing him when presented with a clear danger. Strategically speaking, killing it was a huge lapse in judgement on Haverson's part.