When the vast majority of historians reach the same conclusion on anything, it *is* a consensus.

When people who have *not* learned methods of historiography, studied official documents, soldiers' letters and diaries, other primary sources, and a few hundred historical and critical articles choose to believe something else about history, it isn't a consensus. Instead, it's a myth.

A consensus isn't "just another opinion." It's the considered view of the best-informed researchers, founded on the best evidence available. That means original documents, not poetry, fiction, or movies.
No one has ever questioned the war's unprecedented brutality. But the tons of new documents available in the 1960s (and more in the '90s after the collapse of the USSR) strongly support the original view of 1914-18: Britain (and later America) had to fight, the public understood why, men volunteered in droves (though few imagined what many would face), and the three aggressor nations who launched a bald-faced imperialist war of conquest were soundly and deservedly defeated.

Those are still facts, even if economist Niall Ferguson believes (virtually alone) that a German-Austrian victory *might* not have been a disaster if things worked out according to his informed but still hypothetical scenarios.