Well, it turns out they could, and boy did they. They took all the wealth they could find, killed and raped Christians as they went, stole the statues of horses that now adorn St. Mark's Cathedral in Venice, and retook exactly none of the Holy Land. Thanks, Thought Bubble. So you'd think this disaster would discredit the whole notion of crusading, right? No. Instead, it legitimized the idea that crusading didn't have to be about pilgrimage, that any enemies of the Catholic Church were fair game. Also, the Fourth Crusade pretty much doomed the Byzantine Empire, which never really recovered.