It doesn't take a master of etiquette not to send a recruiter a 4-paragraph explanation of the finer points of POSIX v. UNIX. "I'm right and I'm going to explain to you exactly why whether it's relevant or not" is not generally a good attitude to have in the business world, even if you're working for Facebook.

That actually makes it more problematic. New grads trying to break into an industry should be especially respectful. If someone can't strategically avoid confrontation when the situation calls for it, that does not bode well for their ability to work in a team.

There are many new grads who are capable of appropriately dealing with social challenges. Those who can't have only themselves to blame.

True, but the recruiter on the other hand should show more experience and cognition. The emails might refer to systems the recruiter doesn't understand, but the actual words make complete sense.