Apocalypse WWI: debating the tactics

Watching Apocalypse WWI got me thinking about modern day parallels, how I would realistically react if I found myself in that situation, the insanity of the whole affair, etc.

One question I really wondered about: what kept the troops from mass desertion?

Individual deserters/those who refused to fight were obviously shot by firing squad, but what was the motivation to prevent entire divisions from just saying "frick this"?

Think about your life: at some points of the war you hav less than a 50% chance of survival. You are constantly ordered to go "over the top" by distant generals, to get mowed down by the newly industrialized warfare techniques. A good charge will capture the equivalent of a football field at the cost of several thousand troops. You live in filthy disease ridden muddy open trenches, at constant risk of dying a horrible death from gas, shells, etc. You are also starving and cold. If you are lucky enough to be injured, you will be horribly disfigured for life in many cases. While you are suffering, your officers are living in the chateaus in the rear, eating, smoking, and drinking as part of the class system. Seems like there is no way this could have lasted four years.