Spencer M. answered 08/09/19
Willing to teach the ropes of academic and creative writing!
Essentially, what this passage is communicating is the scout's opinion of the people of the Huron tribe. The character believes that the Huron are fundamentally stupid and evil, with thievish meaning a person who acts like a thief. By "nor do I care by whom they are adopted," the scout is saying that the reason that Hurons are this way is not because of their society, but because of what they are from birth- essentially a racist argument.