This is thoughtful and well-written, and I didn't really like it. I don't think I'm supposed to like it. I'd call it "effectively unpleasant," I think, and it's one of those very unappealing (t0 me) stories where men go off to war and do war crimes and they come back home, still monsters. Because this was first published in F&SF, there's a speculative element which introduces spiritual judgement in the Central American jungle, as well as drugs that turn soldiers into killing machines, but neither of these really does away with the fact that the protagonist is a fairly terrible person, marginally tolerable in comparison to his exceptionally terrible compatriots, and I suppose I should care about his trauma, sent off to a terrible war as he is, but I don't. Burn down villages with everyone still in them, and I don't give a shit about your trauma.