Glad to see someone else saying it, because it's simply a terrible argument for the atheist left to make in light of historical fact. Pol Pot, as an example, was one of the lesser offenders in the new order of despots, and he and his minions slaughtered millions. The worst of religious crusades is like a tiny flea compared to the whale of atheist offenders.
Tu quoque is a fallacy, if you did not know.
Wherever do they get their "facts" about the Crusades? They ignore the whole history of the Middle East prior to the First Crusade. It was occasioned
by the deeds of the Seljuk Turks, who as new converts to Islam, were far less tolerant of Christians than the Arabs had been, and who actively persecuted
pilgrims to the Holy Land. But what led directly to the Crusade was a call for help from the Greek Emperor, whose lands had been overrun by the Turks.