It’s a strange question in the first place because it comes from people who are influenced by an essentially Catholic (Christian) mindset.
Yes, it’s true that the armies of the Crusades invaded the Middle East and Africa, and in the First Crusades, caused some atrocities.
Yet, harsh warfare like displayed in that time period was quite common. And the concept of “human rights” was still in its early phase, being pioneered by the Church at the time, certainly not by the Muslims. It’s funny that nowadays the concept of humanity and “justice” is used against the Church when it was the Church that originated those concepts in the first place. The moralizing influence has been so extensive that people don’t even realized how steeped in it they are.
The very belief that we should preserve human life because it is all precious is not something that the pagan Europeans believed in, nor was it a belief that was accepted in the Middle East and Africa either. And certainly Islam can’t really talk about being peaceful, seeing that the Crusades in the first place were a defensive strike against Muslims that had already conquered three of the five holy Christian patriarchates and besieged a the fourth and fifth (Constantinople, Rome) on more than one occasion.
Sorry, I do not accept these arguments from non-Christians. They have no leg on which to stand.