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People like jkd are the reason I'd advise anyone to run screaming from grad school into the military. Teaching, even at major research universities--ESPECIALLY at major research universities--usually gets short shrift because this attitude of academic puritanism and snobbery is prevalent there. (And depending on what he wants to focus on, some state schools are better than Harvard or Yale.)
There are lots of smart, thoughtful, well-educated veterans posting here on both sides of the question. That's fantastic. There can never be too many. If the culture of the military isn't quite what the LW is used to, his presence there could only help improve it. And I have to say, he'd have a much broader experience of the world and its people than he would in academic culture. But only, however, if his primary motive is to serve his country, rather than to advance his own interests, as a previous commenter pointed out. I was a little disappointed not to see him express such a sentiment in his letter.
That said, my other first thought on reading is also similar to that expressed by other writers. There are many great and honorable people serving in the armed forces. The armed forces, however, does not always treat them as they deserve to be treated for what they've given. I hope that improves over the next several years, but it's still a cause for concern. It's one thing to be willing to face hazardous and extreme working conditions and to put your life potentially in danger. It's another to survive those things only to come home, injured in body and/or spirit, and slip through the cracks because the organization you put your life on the line for used you up and threw you away.