Wilfred Owen - Poetry

Both this poet and this poem are new to me.  The poet is Wilfred Owens and the play is titled 'Dulce et Decorum Est'.  (This is part of a latin phrase that means "it is sweet and proper to die for one's country'.)

Bent double, like old beggars under sacks,
Knock-kneed, coughing like hags, we cursed through sludge
Till on the haunting flares we turned our backs
And towards our distant rest began to trudge.
Men marched asleep. Many had lost their boots
But limped on, blood-shod. All went lame; all blind;
Drunk with fatigue; deaf even to the hoots
Of tired, outstripped Five-Nines that dropped behind.

Gas! Gas! Quick, boys, - An ecstasy of fumbling,
Fitting the clumsy helmets just in time;
But someone still was yelling out and stumbling,
And flound'ring like a man in fire or lime . . .
Dim, through the misty panes and the thick green light,
As under a green sea, I saw him drowning.

In all my dreams, before my helpless sight,
He plunges at me, guttering, choking, drowning.

If in some smother dreams you too could pace
Behind the wagon that we flung him in,
And watch the white eyes writhing hin his face,
His hanging face, like a devil's sick of sin;
If you could hear, at every jolt, the blood
Come gargling from the froth-corrupted lungs,
Obscene as cancer, bitter as the cud
Of vile, incurable sores on innocent tongues,-
My friend, you would not tell with such high zest
The old Lie: Dulce et decorum est
Pro patria mori.

Simple theme here.  The horrors of war are so horrible, the price so high, that patriotic sacrifice is a bad deal.  The book lists the authors lifespan as 1893-1918.  According to Wikipedia, he was English and fought in WWI.  In fact, he died exactly one week before the armistice was signed.  A terrible waste.
The poem is certainly effective.  All wars involve horrors.  The American civil war happened about 50 years earlier and it chewed up people in awful ways.  WWI was in a different league though, in the 'new horrors' department.  This poem describes a gas attack and I'm sure they were surreally awful.  A look back from the future doesn't help because the war led to little good.
However, I want to push back against the main theme.  My chief objection (taught to me by Heinlein) is that this approach becomes dangerous when it becomes widespread.  If highly civilized country A decides that it won't fight and barbarian country B decides that it still will, then who wins?  If you don't want to think about a simple war between two countries, then replace the above question with cultures.
At some point a country (or culture) will find that it is in a situation where it must fight or be utterly defeated, dismantled and enslaved.  It is a source of shame that the Oxford union voted to not fight against Germany.  Meanwhile, the Battle of the Blitz is one of England's proudest moments. 
Which doesn't mean that the broader point of the poem doesn't still have truth.  War is awful and we should try extremely hard to make those situations where countries must fight rare.  I honestly don't know if the approach of this poem is the best one.