The point about illegal retribution is really good. Notice how email #3 walked it right back and came up with an entirely different argument. They knew they screwed up.
Yep. More to the point, when a letter from a lawyer comes in, they're going to ask their lawyer for his opinion, and he is going to say "#$()! Why did you send that!?! That drastically complicates things for me. Just pay the kid or we're going to run up quite the bill fighting him and may yet lose."
(If you don't understand why that email is radioactive, here is a joking-but-not-really exhaustive list of things US courts will find as being sufficient reason for denying employees earned wages: )
