When it comes to Christianity, we know that all the denominations hold one single view in terms of character of Jesus of Nazareth, him being the risen Christ and his teachings of love and many other things. So, irrespective of who is responsible of the crusades, it does leave a "dark mark" in the history of Christianity as a whole, which whether we like it or not, we cannot run from it but have to accept it.
But, when a question is raised about the immorality of the crusades, it is important here to understand that "IT IS NOT THE LOGICAL OUTWORKING OF THE CHRISTIAN FAITH". what I mean is, the crusades, though they were carried in the name of Jesus(Christianity as a whole), never conformed to the teachings of Jesus, but in fact were opposite to that of what Jesus taught. I could give many citations from the verses where Jesus insisted on his followers to love one another, but it is very evident from the bible itself. One such verse that comes to my mind is where Jesus tells his disciples to love one another, this way the world will know that they(his disciples which means even we) are his and he lives in them.(John 13:34-35)
Now, we know that we believe in Jesus because he is the truth, the way and the life. We believe in what the bible describes about Jesus. So, though these crusades which we cannot deny, happened in the name of Jesus, it in no way undermines our belief in Jesus of Nazareth described in the NT. And this must be kept in mind "WHETHER THE ACTIONS CONFORM WITH THE BELIEF THAT IS HELD".
According to me, these Crusades should not impact much on modern Christianity!