Nothing new about this view. Christendom had been fighting a defensive battle against the Muslims for well of 300 years. They had been attacking via the Iberian peninsula, Scily/Italy and though Asia Minor. The goal was no less than the destruction of Christendom. The Crusades, at least the first, was a just attempt (albeit belated) at adopting an offensive strategy. Now, not all of the actions during the Crusades were just. But the idea, in and of itself, was very noble. And although the First Crusade is considered to have ultimately failed with the fail of the Kingdom of Jerusalem in the late 13th century, for 200 years it largely took the battle front out of Christendom and moved it to Muslim lands. Considering, the war between Christendom and the Islamic world really lasted really over 1000 years (an ending could be said to be the victory over the Ottomans at the Seige of Vienna in 1683), that 200 years break was critical to the flowering of Christendom. So I think the failure is overstated.