In the book, The Things They Carried, why do soldiers tell jokes about war, about killing?

From the text, we can infer that telling jokes alleviated the horrors of war. Note, joke telling didn't make the horrors go away, but they did serve to desensitize the boys enough that they were able to go on. Unless you've been in war, it's hard to understand. I haven't been in war, but I do know people who served in Vietnam. They were forever changed.