Remember that you are someday going to have to help the child understand why he or she needed to be separated from those who gave them birth. At this point you will not be discussing theoretical situations. You will be talking about a real child who may become yours. If you are comfortable about the background, you will convey this to the child in a myriad of ways. If you are disgusted by it, your child will feel it and come to feel uncomfortable about himself.
Social workers are human beings too.
Sometimes in their efforts to make certain that a couple can accept a difficult or unpleasant background, they may overemphasize this and neglect to tell you some of the positive facets of the personalities and talents of the birth parents. Be prepared to ask questions that will elicit this information too. What were they able to do before separation became necessary. What talents did they demonstrate. Try to get a picture of them as real live people.