Okay, kiddo, let me explain this to you in a way that makes sense. A long time ago, some people thought it was a good idea to go on a big adventure called a crusade. They wanted to go to faraway places and try to take back control from people who didn't believe the same things they did.
But, not everyone thought this was a good idea. Some people thought it was better to stay home and work on making things better there. They thought that going on a crusade was not the right way to help people, and that there were other ways to make change happen without fighting.
Criticism of crusading means that people are saying that going on a crusade is not a good idea. They are pointing out the problems with fighting and hurting other people to get what you want. They think that it's important to find other ways to solve problems and work together instead.
So, you see, it's like when you and your friends have a disagreement. Do you fight and hurt each other, or do you talk it out and find a way to make everyone happy? The criticism of crusading is saying that talking it out and finding a peaceful solution is a better way to go about things.