I too am a pre washer for allergy issues as well. I just don't understand the thinking behind not washing either before or after making the quilt. This fabric goes into a quilt that will probably be used to wrap up in. These unwashed fabrics will be touching bare skin, and how many of us will pull a quilt up over our heads when we are cold? I would never buy a piece of clothing from anywhere, including retail shops and especially thrift stores and wear it before I put it next to my skin! Why would a quilt be any different?
I am not a germaphobe but I do know that there is some nasty stuff out there and I would want to take any precaution I could to prevent any problems.