Jim, we have the benefit of nearly a hundred years of hindsight.
Did THEY believe in the cause?
That Dublin mob certainly did.

And even from our perspective, The Kaiser presided over a pretty nasty regime. Should they have been allowed to occupy most of the continent?

In the years running up to the war, Sinn Fein went bust lacking any support.
Would hundreds of thousands have marched off to a foreign war, for an implied promise of something they were not even bothered to vote for?