"It's not our lifespans that I'm talking about." Sure they lived longer than humans - by a lot - but these were wreckers they were talking about. Even with the lack of a war here, how long did this kid expect them to live when things eventually went bad.

"Can't protect them if you get crushed in battle, now can you." If she was intending to keep them alive, that would mean that she'd have to follow them into fights... Whenever those happened.

"Humans are very durable, from what I know."

Admittedly, he didn't know much about humans, but it seemed clear enough that they were easy to kill. Didn't have that great armor either.