I agree with most of your reply, but I'd disagree on dark ages and crusades.
The dark ages were indeed a time of cultural collapse: science largely stopped, state capacity was cut massively (one indicator being that the Romans used to field armies of hundreds of thousands and the successor states in Europe would wage war with a few thousand men), large public infrastructure projects disappeared, religion started wielding a stifling influence on all aspects of life and society. Depending on who you ask, people will tell you that things improved for the ordinary people or very much worsened.
History, like other fields in academia, undergoes cyclical periods of rejection of dogma, as new researchers try to make a name for themselves by turning on their predecessors: I see the rejection of Dark Ages in the last decades as largely that, and recently there is more of a reversal, with new Middle Ages researchers turning on those previous researchers.
For crusades: this was not an answer to conquest. Byzantium had lost its crown jewel, modern Turkey, to Turks and then Arabs (a region, by the way, that had been reconquered and lost for centuries). The emperor at the time, Alexios, wanted a few hundred Western knights, to help him reconquer a few cities in the region (Jerusalem was not part of his plans, or at least priorities, religion was very much not a variable in his calculations), but the pope at the time saw a way to increase his own power and stirred up a religious hysteria: when the Western armies arrived to Constantinople, the Byzantines were surprised by the size and the goals of them, conflicts happened immediately, and the entire story of the first crusade is the emperor trying to conquer some revenue-generating lands and distrusting the Westerners, while the Western princes wanted to generate revenue for themselves (on my phone, simplified). Over further crusades, the Byzantines started to hate the 'Franks' (Westerners), as did the 'liberated' cities, for the many crimes and massacres they committed. Religion, and helping the fellow Christians, was simply a weapon wielded by the pope, the emperor, and the princes.
I think the rest of that previous comment is bigotry, but the poster is right about Crusades being a shameful event in the history of Christianity.