I don't even think they are particularly understandable, not in the sense you mean. Alexius wanted a regiment or two's worth of crack troops, the Pope preached it as a holy duty, hoping to get enough soldiers to go without having to pay them, and ended up getting a mass migration. No one expected it, no one asked for it.I simply said they were understandable. Not everything understandable is also justified.
I'm not sure that anyone could have predicted the response, especially the Children's Crusade. It is understandable to me that Urban II capitalized on a chance to gain political power while bringing Europe closer to unity, reducing warfare between confessing Christians, and retaking land that had been lost to non-Christians. I can see how to a pope of that time, it would have seemed like a good idea. That doesn't justify it, however - even if it wouldn't have run out of control, and even if he hadn't perverted the Gospel in the process of launching it.I don't even think they are particularly understandable, not in the sense you mean. Alexius wanted a regiment or two's worth of crack troops, the Pope preached it as a holy duty, hoping to get enough soldiers to go without having to pay them, and ended up getting a mass migration. No one expected it, no one asked for it.