A few thoughts:
1) First, the wording of the letter appears to be that of Michael Moore.
2) Is it correct that the young soldier was his parents only child? If so, I seem to recall that during the draft days, if a man had no siblings, the government did not require him to enlist.
3) While a mother's grief is always respected, Mrs. Sheehan must understand that her son made the decision on his own to enlist in the Armed Forces. And, believe me, when one visits any Armed Forces recruitment center, they are told in no uncertain terms that the military is a fighting, killing machine. No person (Sheehan's son included) enlists without full knowledge that they could die on the job.
Peace.
Perhaps her only son. She may have a couple of daughters.