Actually the poem is:
"It is the Soldier, not the minister
Who has given us freedom of religion.
It is the Soldier, not the reporter
Who has given us freedom of the press.
It is the Soldier, not the poet
Who has given us freedom of speech.
It is the Soldier, not the campus organizer
Who has given us freedom to protest.
It is the Soldier, not the lawyer
Who has given us the right to a fair trial.
It is the Soldier, not the politician
Who has given us the right to vote.
It is the Soldier who salutes the flag,
Who serves beneath the flag,
And whose coffin is draped by the flag,
Who allows the protester to burn the flag."
and it's by Charles M. Province, US Army vet.
I just checked some sources, because I had seen both before. Father O'Brien always denied the fact that he wrote it (and he was in the USMC, but as a Sergeant and became a Father after he got out).